Question

How do you verify `cos ^2 u - sin ^2 u = 2 cos^2 u -1`?

Answer 1

We know that `sin^2u + cos^2 u =1`

Explanation:

LHS= - (`sin^2u - cos^2 u`)
= - {`(1-cos^2u) - cos^2 u`} [ since `sin^2u + cos^2 u =1`]
=`2cos^2u-1`
=RHS

Hence proved