int x^2 * e^(x^3) dx = int e^(x^3) d(1/3 * x^3) = 1/3 * int e^(x^3) d(x^3) =
= | t = x^3 | = 1/3 * int e^t dt = 1/3 * e^t + C = | t = x^3 | = 1/3 * e^(x^3) + C