I need some help. I've watched a video that explained a similar problem, but it never showed any subtraction of integrals in the explanation. Nothing about subtracting integrals is in the textbook either.

Yes, this is homework. I'm not here for anyone to do it, but the $\displaystyle \int 75cos^2 x sinx dx - \int (?) dx$ is really confusing me. Can someone explain what is happening?