Hi If I have the indefinite integral x(sqrt(4-x^2))dx must I replace x with 2sint and then dx = 2cosdt or can I just do regular substitution with u = 4-x^2 since xdx occurs in the integral already. when I solve it this way I get -1/3(4-x^2)^3/2 + C it just seems alot more work to do it the trigonometric substitituon way. Any help is much appreciated. Thanks!!