1. The problem statement, all variables and given/known data ∫ Sinx cos x dx 2. Relevant equations 3. The attempt at a solution If you integrate it using substitution, you get -cos2(x)/2but if you use double angle formula to rewrite the problem, it will be ∫1/2 sin(2x), and integrate it, you get -cos(2x)/4. isn't it weird?