Cho plus number has the first class$$u_1=-2,\ d=3 $${bạn}_{}=-2,đ=3$$ . Tính${\mathrm{<span\; class="katex-container"\; data-idx="3"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="3"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}$bạn_{10} $${bạn}_1$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2.</span></span></span></span>}{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}}^{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">9</span></span></span></span>}}$u_{10}=-2.3^9 $${bạn}_1=-2.3^9$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">25</span></span></span></span>}$u_{10}=25 $${bạn}_1=25$$

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\phải) $$\left({bạn}_{}\right)$$ có${\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\frac{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">số\; 8</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">26</span></span></span></span>}$u_1=\frac{1}{3},\ \ u_8=26 $${bạn}_{}=\frac{}{3},{bạn}_{}=26$$ . Sai lầm tìm kiếm d

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\frac{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">11</span></span></span></span>}}{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}}$d=\frac{11}{3} $$đ=\frac{1}{3}$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\frac{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}}$d=\frac{10}{3} $$đ=\frac{1}{3}$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\frac{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}}{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}$d=\frac{3}{10} $$đ=\frac{}{10}$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\frac{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}}{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">11</span></span></span></span>}}$d=\frac{3}{11} $$đ=\frac{}{11}$$

Cho bốn số: 2; một ; 6; b theo thứ tự là cấp số cộng. ab Tính

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">một</span></span></span></span>}\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">b</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">32</span></span></span></span>}$ab=32 $$mộtb=32$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">một</span></span></span></span>}\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">b</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">40</span></span></span></span>}$ab=40 $$mộtb=40$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">một</span></span></span></span>}\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">b</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">12</span></span></span></span>}$ab=12 $$mộtb=12$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">một</span></span></span></span>}\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">b</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">22</span></span></span></span>}$ab=22 $$mộtb=22$$

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\right) $$\left({bạn}_{}\right)$$ có${\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">4</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">4</span></span></span></span>}$u_4=2,\ \ u_2=4 $${bạn}_{}=2,{bạn}_{}=4$$ . Tính${\mathrm{<span\; class="katex-container"\; data-idx="2"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="2"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}$u_1 $${bạn}_{}$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">6</span></span></span></span>}$u_1=6 $${bạn}_{}=6$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}$u_1=1 $${bạn}_{}=1$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">5</span></span></span></span>}$u_1=5 $${bạn}_{}=5$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}$u_1=-1 $${bạn}_{}=-1$$

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\right) $$\left({bạn}_{}\right)$$ has a total index${\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}$u_n=3n-2 $${bạn}_{}=3n-2$$ . Sai lầm tìm kiếm d

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}$d=3 $$đ=3$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}$d=2 $$đ=2$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}$d=-2 $$đ=-2$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}$d=-3 $$đ=-3$$

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\phải) $$\left({bạn}_{}\right)$$ có${\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>$u_1=3, $${bạn}_{}=3,$$ sai công$\mathrm{<span\; class="katex-container"\; data-idx="2"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="2"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="2"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">4.</span></span></span></span>}$đ=4. $$đ=4.$$ biết${\mathrm{<span\; class="katex-container"\; data-idx="3"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">S</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="3"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="3"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="3"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">253</span></span></span></span>}$S_n=253 $$S_{}=253$$ . Find n.

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">9</span></span></span></span>}$n=9 $$N=9$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}$n=10 $$N=10$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">11</span></span></span></span>}$n=11 $$N=11$$

• $\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">12</span></span></span></span>}$n=12 $$N=12$$

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\phải) $$\left({bạn}_{}\right)$$ có${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">4</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">+</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">6</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">26</span></span></span></span>}$u_1=10,\ u_4+u_6=26 $${bạn}_{}=10,{bạn}_{}+{bạn}_{}=26$$ . Unknown public d's integer.

$\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}$d=-3 $$đ=-3$$

$\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">3</span></span></span></span>}$d=3 $$đ=3$$

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\right) $$\left({bạn}_{}\right)$$ có${\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">5</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">15</span></span></span></span>}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">20</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">60.</span></span></span></span>}$u_5=-15,\ \ u_{20}=60. $${bạn}_{}=-15,{bạn}_2=60.$$ Tính${\mathrm{<span\; class="katex-container"\; data-idx="2"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">S</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="2"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}$S_{10} $$S_1$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">S</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">125</span></span></span></span>}$S_{10}=-125 $$S_1=-125$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">S</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">250</span></span></span></span>}$S_{10}=-250 $$S_1=-250$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">S</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">200</span></span></span></span>}$S_{10}=200 $$S_1=200$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">S</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">200</span></span></span></span>}$S_{10}=-200 $$S_1=-200$$

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\phải) $$\left({bạn}_{}\right)$$ biết${\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span><span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">5</span></span></span></span>}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="1"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}$u_1=-5,\ d=2 $${bạn}_{}=-5,đ=2$$ . Number 81 is a subNUMX number?

• 100

• 50

• 75

• 44

Cho cấp số cộng$<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>$\left(u_n\phải) $$\left({bạn}_{}\right)$$ . Định nghĩa nào sau đây là sai?

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">+</span></span></span></span><span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">(</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">-</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">)</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">\forall </span></span></span></span>}\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">\ge </span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}$u_n=u_1+\left(n-1\right)d,\ \ \ \forall n\ge2 $${bạn}_{}={bạn}_{}+\left(n-1\right)đ,\forall n\ge 2$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">+</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">+</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">đ</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">,</span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">\forall </span></span></span></span>}\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">N</span></span></span></span>}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">\ge </span></span></span></span>\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}$u_{n+1}=u_n+d,\ \ \forall n\ge1 $${bạn}_{n+}={bạn}_{}+đ,\forall n\ge 1$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">5</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\frac{{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">+</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">9</span></span></span></span>}}}{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}}$u_5=\frac{u_1+u_9}{2} $${bạn}_{}=\frac{{bạn}_{}+{bạn}_{}}{2}$$

• ${\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">5</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">=</span></span></span></span>\frac{{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">1</span></span></span></span>}}<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">+</span></span></span></span>{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">bạn</span></span></span></span>}}_{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">10</span></span></span></span>}}}{\mathrm{<span\; class="katex-container"\; data-idx="0"\; contenteditable="false"><span\; class="katex-display"><span\; class="katex"><span\; class="katex-mathml">2</span></span></span></span>}}$u_5=\frac{u_1+u_{10}}{2} $${bạn}_{}=\frac{{bạn}_{}+{bạn}_1}{2}$$