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.