Primitive of Power of x by Exponential of a x/Examples

Examples of Use of Primitive of $x^n e^{a x}$

Primitive of $x^3 e^{-x}$

$\ds \int x^3 e^{-x} \rd x = -e^{-x} \paren {x^3 + 3 x^2 + 6 x + 6} + C$