1. The problem statement, all variables and given/known data find the following integral: cos(x/2) - sin(3x/2) dx 2. Relevant equations I think the substitution method has to be used. Solve integrals by parts. 3. The attempt at a solution Let u = x/2 cosu du/dx=1/2, I then inverted it so dx/du = 2/1 = 2 So dx=2du Now I have cosu2du Do I take out the constant ie: constant multiple rule? I am not confident about where to go next. Any help would be vastly appreciated, thank you.