Applying and analysing trigonometric functions

Find the exact value of the expression.
cos(20)cos(40) - sin(20)sin(40)

• 1/4
• 1/2
• √(3)/2
• √(3)

 $\cos57\degree\sin55\degree$  

•  $\frac{\cos112\degree-\cos2\degree}{2}$  

•  $\frac{\sin112\degree-\sin2\degree}{2}$  

•  $\frac{\sin2\degree+\sin112\degree}{2}$  

•  $\frac{\sin112\degree-\cos\ 2\degree}{2}$  

Cos ( x-y)

• Cos x cos y + cos x cos y

• Cos x sin y+ cos x sin y

• Cos x cos y - sin x sin y

• Cos x cos y + sin x sin y

Sin A =

• 2 sin ( A/2) cos ( A/2)

• - cos A sin A

• [2 tan(A/2)] / 1+ tan² ( A/2)

• 2sin²A

What is the exact value of  $\tan\left(\frac{2\pi}{3}\right)$  

•  $\frac{2}{\sqrt{3}}$  

•  $\frac{\sqrt{2}}{2}$  

•  $-\sqrt{3}$  

•  $-\frac{\sqrt{3}}{3}$