Question #3fa40

1 Answer
May 18, 2017

see below

Explanation:

cos^2 X - sin^2 X = 2 cos^2 X -1

we use LHS to prove RHS
we know that,
sin^2 X + cos^2 X = 1, then
sin^2 X = 1 - cos^2 X

therefore
cos^2 X - sin^2 X = cos^2 X - (1 - cos^2 X)

cos^2 X - sin^2 X = cos^2 X -1 +cos^2 X

cos^2 X - sin^2 X = 2cos^2 X -1 -->proved