Math Help - derivative of xe^(-x)

When I use the product rule to find the derivative of

xe^(-x) I get

xe^(-x) + e^(-x) but the correct answer is y'=(1-x)e^(-x)

which is e^(-x) - xe^(-x)

why am I getting a plus when the answer is a minus?

Hey kingsolomonsgrave.

Recall that d/dx e^(-x) = -e^(-x).

oh! thanks