Well guys, I really would appreciate it were someone able to prove to me this:
cos^2x-sin^2x = (1-tan^2x)/(1+tan^2x)
I think the left side equals cos(2x), but I'm not even sure of that! Any help is much appreciated!
You're correct about the left side of the equation, but that isn't going to help you any. Just use the identity on the right side of the equation. If you simplify the fraction, you'll obtain the left side: