Sum, Difference, and Double Angle Identities

Use Sum or Difference Identities to find the exact value of the expression:
cos(75°)

• 1/4
• ( √(6) - √(2) ) / 4
• (√(6) + √(2)) / 4
• (-√(6) - √(2)) / 4

solve
cos(π/3)cos(2π/3)-sin(π/3)sin(2π/3)

• 1
• -1
• 1/2
• -1/2

Find the exact value of  $\sin2x$    if  $\sin x=\frac{12}{13}$   and x is in the first quadrant. 

•  $\frac{120}{169}$  

•  $\frac{25}{169}$  

•  $\frac{60}{169}$  

•  $\frac{5}{13}$  

If A and B are first quadrant angles with sinA=15/17 and cosB=4/5, find cos(A - B).

• 3/8

• 8/17

• -13/85

• 77/85

 $If\ \sin\theta\ =\ \frac{4}{5},\ where\ 0\le\theta\le\frac{\pi}{2},find\ \sin2\theta$  

•  $\frac{12}{25}$  

•  $\frac{24}{25}$  

•  $-\frac{24}{25}$  

•  $\frac{3}{5}$  

 $If\ \cos\theta\ =\ \frac{3}{5},\ where\ 0\le\theta\le\frac{\pi}{2},find\ \cos2\theta$  

•  $\frac{12}{25}$  

•  $\frac{24}{25}$  

•  $-\frac{7}{25}$  

•  $\frac{7}{25}$  

If cosx = - 4/5, find secx.

• -5/4

• -3/5

• 5/3

• √3/2