Math Help - [SOLVED] derivative question

1. [SOLVED] derivative question

If y= cos^2[x]-sin^2[x] then y'=

I know how to do it if the exponent is after the x, but how would this be done? The answer key says -2sin(2x). Thanks

2. Originally Posted by jst706
If y= cos^2[x]-sin^2[x]
Note that $\cos^2x-\sin^2x=\cos2x,$ now take the derivative.