What is the integral of (x^3)/(e^{2x)} ?

The integral of (x^3)/(e^{2x)} is 1/16 (-8e^{-2x}x^3-3(4e^{-2x}x^2-2(-2e^{-2x}x-e^{-2x})))+C

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integral of (x^3)/(e^{2x)}

\int \frac{x ^{3}}{e ^{2 x}} d x

\frac{1}{16} (- 8 e^{- 2 x} x^{3} - 3 (4 e^{- 2 x} x^{2} - 2 (- 2 e^{- 2 x} x - e^{- 2 x}))) + C

Solution steps

\int \frac{x ^{3}}{e ^{2 x}} d x

Apply exponent rule:

\frac{1}{a ^{b}} = a^{- b}

\frac{x ^{3}}{e ^{2 x}} = (x^{3}) e^{- 2 x}

= \int x^{3} e^{- 2 x} d x

Apply u-substitution

= \int \frac{e ^{u} u ^{3}}{16} d u

Take the constant out:

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

= \frac{1}{16} \cdot \int e^{u} u^{3} d u

Apply Integration By Parts

= \frac{1}{16} (u^{3} e^{u} - \int 3 u^{2} e^{u} d u)

\int 3 u^{2} e^{u} d u = 3 (u^{2} e^{u} - 2 (e^{u} u - e^{u}))

= \frac{1}{16} (u^{3} e^{u} - 3 (u^{2} e^{u} - 2 (e^{u} u - e^{u})))

Substitute back

u = - 2 x

= \frac{1}{16} ((- 2 x)^{3} e^{- 2 x} - 3 ((- 2 x)^{2} e^{- 2 x} - 2 (e^{- 2 x} (- 2 x) - e^{- 2 x})))

Simplify

\frac{1}{16} ((- 2 x)^{3} e^{- 2 x} - 3 ((- 2 x)^{2} e^{- 2 x} - 2 (e^{- 2 x} (- 2 x) - e^{- 2 x}))) : \frac{1}{16} (- 8 e^{- 2 x} x^{3} - 3 (4 e^{- 2 x} x^{2} - 2 (- 2 e^{- 2 x} x - e^{- 2 x})))

= \frac{1}{16} (- 8 e^{- 2 x} x^{3} - 3 (4 e^{- 2 x} x^{2} - 2 (- 2 e^{- 2 x} x - e^{- 2 x})))

Add a constant to the solution

= \frac{1}{16} (- 8 e^{- 2 x} x^{3} - 3 (4 e^{- 2 x} x^{2} - 2 (- 2 e^{- 2 x} x - e^{- 2 x}))) + C

What is the integral of (x^3)/(e^{2x)} ?
The integral of (x^3)/(e^{2x)} is 1/16 (-8e^{-2x}x^3-3(4e^{-2x}x^2-2(-2e^{-2x}x-e^{-2x})))+C