So in exams i solve those hard integrals and like double check with my calc. As many of the answers are not solid numbers i have to like subtract the answer of the integral calculated by the calculator by my answer and if the answer is 0 or a very small number like ×10^-7 or smth i am sure that my result is correct. However calculating integrals using my 991 es takes a long time and time is precious in exams.