Chain rule differentiation

1. Jun 16, 2014

grace77

The question:

This is the solution that was given by my teacher

Attempt:

I understand how the work is done until the 3-4 line. Where did the 1-cos2x disappear to in the 4th line?
I know you can use the outside inside method but try as I might, I can't seem to understand how the final answer was gotten??

Can someone please tell me what I'm missing here??

2. Jun 16, 2014

D H

Staff Emeritus
What is $(1+\cos(2x)) + (1-\cos(2x))$ ?

3. Jun 16, 2014