Anyway, the formula you gave is if A and B are both variables right? What about in the case that one is a variable and the other is a contant? Do I just treat the constant as a variable and plug it through?
Ignore the outer integral and do the inner one first.
You can treat x as a constant here. Let . Don't forget to change the integration limits. Then you can plug this in the outer integral and the rest is easy..
Also you can use the trigonometric addition formula and Fubini's theorem.