# Homework Help: Trig identities?

1. Apr 19, 2010

### Jenkz

1. The problem statement, all variables and given/known data
How to get from

$$\sqrt{2+2cosx}$$
to

2cos(x/2)

3. The attempt at a solution

I'm pretty much stuck on this.
I can only see that is simplifies by taking out the common factor 2, which isnt correct.

2. Apr 19, 2010

### rock.freak667

Well id cos2x=2cos2x-1, then cosx=2cos2(x/2)-1

3. Apr 20, 2010

Yup, thanks!