What is the integral of x^2*4^{-x} ?

The integral of x^2*4^{-x} is -(2^{-2x-1}x^2)/(ln(2))-1/(ln^2(2))*2^{-2x-1}x-1/(ln^3(2))*2^{-2x-2}+C

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integral of x^2*4^{-x}

\int x^{2} \cdot 4^{- x} d x

- \frac{2 ^{- 2 x - 1} x ^{2}}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{- 2 x - 1} x - \frac{1}{ln ^{3} ( 2 )} \cdot 2^{- 2 x - 2} + C

Solution steps

\int x^{2} \cdot 4^{- x} d x

Apply u-substitution

: \int - 4^{u} u^{2} d u

= \int - 4^{u} u^{2} d u

Take the constant out:

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

= - \int 4^{u} u^{2} d u

Apply Integration By Parts

: \frac{2 ^{2 u - 1} u ^{2}}{ln ( 2 )} - \int \frac{4 ^{u} u}{ln ( 2 )} d u

= - (\frac{2 ^{2 u - 1} u ^{2}}{ln ( 2 )} - \int \frac{4 ^{u} u}{ln ( 2 )} d u)

\int \frac{4 ^{u} u}{ln ( 2 )} d u = \frac{1}{ln ( 2 )} (\frac{2 ^{2 u - 1} u}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{2 u - 2})

= - (\frac{2 ^{2 u - 1} u ^{2}}{ln ( 2 )} - \frac{1}{ln ( 2 )} (\frac{2 ^{2 u - 1} u}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{2 u - 2}))

Substitute back

u = - x

= - (\frac{2 ^{2 (- x) - 1} ( - x ) ^{2}}{ln ( 2 )} - \frac{1}{ln ( 2 )} (\frac{2 ^{2 (- x) - 1} ( - x )}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{2 (- x) - 2}))

Simplify

- (\frac{2 ^{2 (- x) - 1} ( - x ) ^{2}}{ln ( 2 )} - \frac{1}{ln ( 2 )} (\frac{2 ^{2 (- x) - 1} ( - x )}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{2 (- x) - 2})) : - \frac{2 ^{- 2 x - 1} x ^{2}}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{- 2 x - 1} x - \frac{1}{ln ^{3} ( 2 )} \cdot 2^{- 2 x - 2}

= - \frac{2 ^{- 2 x - 1} x ^{2}}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{- 2 x - 1} x - \frac{1}{ln ^{3} ( 2 )} \cdot 2^{- 2 x - 2}

Add a constant to the solution

= - \frac{2 ^{- 2 x - 1} x ^{2}}{ln ( 2 )} - \frac{1}{ln ^{2} ( 2 )} \cdot 2^{- 2 x - 1} x - \frac{1}{ln ^{3} ( 2 )} \cdot 2^{- 2 x - 2} + C

f (x) = x^{2}, (0, - 25)

\int 2 x^{2} + 2 d x

\int csc^{7} (x) d x

\int (\frac{3}{2})^{2} d x

f (x) = x^{4} - 18 x^{2} + 81, at x = - 2

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