I'm reading Introductory quantum mechanics written by liboff. When I solve problems, I stuck with calculation such as Intergral(-inf to +inf) e^(-x^2)dx, Intergral(-inf to +inf) (x^2) e^(-x^2)dx, and other many integrals. I studied thomas' calculus but I think I haven't seen these in the book. So can't do it. Are there math books about these integrals? What math subject is related to these (high level?)integrals?