What is the integral of xe^{9-x} ?

The integral of xe^{9-x} is -e^{9-x}x-e^{9-x}+C

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integral of xe^{9-x}

\int x e^{9 - x} d x

- e^{9 - x} x - e^{9 - x} + C

Solution steps

\int x e^{9 - x} d x

Apply u-substitution

= \int - e^{u} (- u + 9) d u

Take the constant out:

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

= - \int e^{u} (- u + 9) d u

Apply Integration By Parts

= - (e^{u} (- u + 9) - \int - e^{u} d u)

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

= - (e^{u} (- u + 9) - (- e^{u}))

Substitute back

u = 9 - x

= - (e^{9 - x} (- (9 - x) + 9) - (- e^{9 - x}))

Simplify

- (e^{9 - x} (- (9 - x) + 9) - (- e^{9 - x})) : - e^{9 - x} x - e^{9 - x}

= - e^{9 - x} x - e^{9 - x}

Add a constant to the solution

= - e^{9 - x} x - e^{9 - x} + C

What is the integral of xe^{9-x} ?
The integral of xe^{9-x} is -e^{9-x}x-e^{9-x}+C