int (0 1) x^2 * (x - 3) dx = int (0 1) (x^3 - 3 * x^2) dx =
= (1/4 * x^4 - x^3)_{0}^{1} = (1/4 * 1^4 - 1^3) - (1/4 * 0^4 - 0^3) =
= 1/4 - 1 = -3/4