Sin^2 x - cos^2 x = 2 sin^2 x - 2

Sin^2 x - cos^2 x = 2 sin^2 x - 1

What do YOU think ?
While we're happy to HELP we won't do all the work for you.
Show us what you have done and where you are having problems..

You need to memorize and use the basic identity sin^2x + cos^2x = 1, and its alternative forms sin^2x = 1-cos^2x and cos^2x = 1 - sin^2x.