# Thread: Verifying an Identity (help)

1. ## Verifying an Identity (help)

could someone show the steps to verifying this identity, and what was used to solve it?

(cos x − sec x)2 = tan2 x − sin2 x

2. ## Re: Verifying an Identity (help)

just expand the LHS we get LHS = cos^2 - 2 cos x * sec x + sec ^2 x = 1-sin^2x -2 + 1 + tan^2 x and you have the RHS

3. ## Re: Verifying an Identity (help)

alternatively you could start with RHS = tan^2x - sin^2x = ( sec^2x - 1 ) - ( 1 - cos^2x) = sec^2x - 2 + cos^2x = sec^2x - 2 secx * cosx+ cos^2x = ( cosx - se x )^2 = LHS