What is the integral from-8 to 4 of sqrt(32-4x-x^2) ?

The integral from-8 to 4 of sqrt(32-4x-x^2) is 18pi

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integral from-8 to 4 of sqrt(32-4x-x^2)

\int_{- 8}^{4} 32 - 4 x - x^{2} d x

18 π

Decimal

56.54866 \dots

Solution steps

\int_{- 8}^{4} 32 - 4 x - x^{2} d x

Complete the square

32 - 4 x - x^{2} : - (x + 2)^{2} + 36

= \int_{- 8}^{4} - (x + 2)^{2} + 36 d x

Apply u-substitution

: \int_{- 6}^{6} - u^{2} + 36 d u

= \int_{- 6}^{6} - u^{2} + 36 d u

Apply Trigonometric Substitution

: \int_{- \frac{π}{2}}^{\frac{π}{2}} 36 cos^{2} (v) d v

= \int_{- \frac{π}{2}}^{\frac{π}{2}} 36 cos^{2} (v) d v

Take the constant out:

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

= 36 \cdot \int_{- \frac{π}{2}}^{\frac{π}{2}} cos^{2} (v) d v

Rewrite using trig identities

= 36 \cdot \int_{- \frac{π}{2}}^{\frac{π}{2}} \frac{1 + cos ( 2 v )}{2} d v

Take the constant out:

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

= 36 \cdot \frac{1}{2} \cdot \int_{- \frac{π}{2}}^{\frac{π}{2}} 1 + cos (2 v) d v

Apply the Sum Rule:

\int f (x) \pm g (x) d x = \int f (x) d x \pm \int g (x) d x

= 36 \cdot \frac{1}{2} (\int_{- \frac{π}{2}}^{\frac{π}{2}} 1 d v + \int_{- \frac{π}{2}}^{\frac{π}{2}} cos (2 v) d v)

\int_{- \frac{π}{2}}^{\frac{π}{2}} 1 d v = π

\int_{- \frac{π}{2}}^{\frac{π}{2}} cos (2 v) d v = 0

= 36 \cdot \frac{1}{2} (π + 0)

Simplify

36 \cdot \frac{1}{2} (π + 0) : 18 π

= 18 π

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What is the integral from-8 to 4 of sqrt(32-4x-x^2) ?
The integral from-8 to 4 of sqrt(32-4x-x^2) is 18pi