Question

Solve Cos^2(5pi/12) using double angle rules.

I've looked up double angle rules online but nothing has helped thus far

Answer 1

cos^2 x = 1+cos2x/2

cos^2 5pi/12 = 1+cos 5pi/6 / 2

= [1+ (-√3/2)]/2

= [2 - √3]/4

Hope this helps