Hi, We were going over trigonometric integration in Calculus II the other day. I got the basic idea, but get lost when we're doing the u-substitution. We had a problem like this: [tex]\int cos^3 (x) dx[/tex] Then we did: [tex]\int (1 - sin^2 (x)) cos(x) dx[/tex] Starting u-substitution: [tex]u = sin(x)[/tex] And [tex]du = cos(x) dx[/tex] So then we have: [tex]\int (1 - u^2) du[/tex] All reasonable so far. But then, du just kind of disappears. [tex]u - u^3/3[/tex] Which is [tex]sin(x) - 1/3 sin^3 (x) + c[/tex] I see how u-substitution works when its something simple, but I can't see how the answer here can be derived to get what was given before.