Question

How do you find the value of `cos 2*(theta)` using the double angle identity?

Answer 1

Refer to explanation

Explanation:

Well we know that

`cos(a+b)=cosa*cosb-sina*sinb`

if `a=b` then we have

#cos(a+a)=cosa*cosa-sina*sina=cos^2a-sin^2a=> cos2a=cos^2a-sin^2a#