x2dx

1. Integrate sqrt ( 4 -x^2)dx

Hi, Can anyone help me integrate : Integral sqrt ( 4 - x^2) dx Some ideas: Make a subsitution x2 = cos (theta) Taking the derivative of both sides: 2x = - sin (theta).d(theta) or.... Double angle identity: (Cosx)^2 = 1 + cos2x / 2 Can anybody give some ideas.