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?

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- December 13th 2012, 08:25 PMkingsolomonsgravederivative 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? - December 13th 2012, 08:34 PMchiroRe: derivative of xe^(-x)
Hey kingsolomonsgrave.

Recall that d/dx e^(-x) = -e^(-x). - December 13th 2012, 08:36 PMkingsolomonsgraveRe: derivative of xe^(-x)
oh! thanks