What is the integral of 3xe^{-3x} ?

The integral of 3xe^{-3x} is -e^{-3x}x-1/3 e^{-3x}+C

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integral of 3xe^{-3x}

\int 3 x e^{- 3 x} d x

- e^{- 3 x} x - \frac{1}{3} e^{- 3 x} + C

Solution steps

\int 3 x e^{- 3 x} d x

Take the constant out:

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

= 3 \cdot \int x e^{- 3 x} d x

Apply u-substitution

= 3 \cdot \int \frac{e ^{u} u}{9} d u

Take the constant out:

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

= 3 \cdot \frac{1}{9} \cdot \int e^{u} u d u

Apply Integration By Parts

= 3 \cdot \frac{1}{9} (e^{u} u - \int e^{u} d u)

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

= 3 \cdot \frac{1}{9} (e^{u} u - e^{u})

Substitute back

u = - 3 x

= 3 \cdot \frac{1}{9} (e^{- 3 x} (- 3 x) - e^{- 3 x})

Simplify

3 \cdot \frac{1}{9} (e^{- 3 x} (- 3 x) - e^{- 3 x}) : - e^{- 3 x} x - \frac{1}{3} e^{- 3 x}

= - e^{- 3 x} x - \frac{1}{3} e^{- 3 x}

Add a constant to the solution

= - e^{- 3 x} x - \frac{1}{3} e^{- 3 x} + C

What is the integral of 3xe^{-3x} ?
The integral of 3xe^{-3x} is -e^{-3x}x-1/3 e^{-3x}+C