how would i find the anti-derv. of (cos(2x)). im really confused with sub. ok i'll use u-du u = 2x du = 2 dx dx = 1/2 du k so... cos(u)*dx since the dx is there, you plug in the dx that i found right? so... sin(2x)1/2 ok so that's a simple integration problem, can someone give me a harder problem and show me how to find "dx", that's what im really confused about.