Question

How do you use the half angle identity to find exact value of cos 15 degrees?

Answer 1

`cos(15^o)` is in Quadrant I which means the answer must be a positive value. Use the half-angle formula to solve it.

Explanation:

`cos(30^o/2)=sqrt((1+cos(30^o))/2` `= sqrt((1+sqrt(3)/2)/2`

`=sqrt((2+sqrt3)/4)~~0.966`

hope that helped