What is the integral of xe^{-kx} ?

The integral of xe^{-kx} is 1/(k^2)(-ke^{-kx}x-e^{-kx})+C

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integral of xe^{-kx}

\int x e^{- k x} d x

\frac{1}{k ^{2}} (- k e^{- k x} x - e^{- k x}) + C

Solution steps

\int x e^{- k x} d x

Apply u-substitution

: \int \frac{e ^{u} u}{k ^{2}} d u

= \int \frac{e ^{u} u}{k ^{2}} d u

Take the constant out:

\int a \cdot f (x) d x = a \cdot \int f (x) d x

= \frac{1}{k ^{2}} \cdot \int e^{u} u d u

Apply Integration By Parts

: e^{u} u - \int e^{u} d u

= \frac{1}{k ^{2}} (e^{u} u - \int e^{u} d u)

\int e^{u} d u = e^{u}

= \frac{1}{k ^{2}} (e^{u} u - e^{u})

Substitute back

u = - k x

= \frac{1}{k ^{2}} (e^{- k x} (- k x) - e^{- k x})

Simplify

= \frac{1}{k ^{2}} (- k e^{- k x} x - e^{- k x})

Add a constant to the solution

= \frac{1}{k ^{2}} (- k e^{- k x} x - e^{- k x}) + C

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What is the integral of xe^{-kx} ?
The integral of xe^{-kx} is 1/(k^2)(-ke^{-kx}x-e^{-kx})+C