# Trig sub

1. Oct 21, 2008

### Sheneron

1. The problem statement, all variables and given/known data

Integral of sqrt(1-x^2) dx

I subbed in sin(Theta) for x, and did my work and got the integral down to: cos(Theta)^2 dTheta.

The problem I am having is integrating cos(Theta)^2. I could use a half angle formula, but the problem is I have to rewrite theta in terms of x, and if I use have angle I end up with Cos(2Theta), which I don't know how to convert back in to x. Please help.

2. Oct 21, 2008

### Sheneron

Nevermind...

Found out the trig property I needed.

sin(2x) = 2sin(x)cos(x)