integrate x*e^x
Let's compute the integral: ∫(xex)dx
For xex, we use integration by parts: ∫(u1·v2')dx = u1·v2 + ∫(u1'·v2)dx, with u1 = x and v2' = ex
So u1' is equal to 1
Let's integrate v2': ∫(ex)dx
ex
Let's compute the integral u1·v2 + ∫(u1'·v2)dx: xex -∫(ex)dx
xex -ex
You can factorize this expression into: ex·(x -1)
Indefinite integrals are defined up to an additive constant C, so this yields: ex·(x -1) + C
Result:   ex·(x -1) + C, where C is a constant