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