What is the integral from 0 to pi of cos^4(5x) ?

The integral from 0 to pi of cos^4(5x) is (3pi)/8

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integral from 0 to pi of cos^4(5x)

\int_{0}^{π} cos^{4} (5 x) d x

\frac{3 π}{8}

Decimal

1.17809 \dots

Solution steps

\int_{0}^{π} cos^{4} (5 x) d x

Apply u-substitution

: \int_{0}^{5 π} cos^{4} (u) \frac{1}{5} d u

= \int_{0}^{5 π} cos^{4} (u) \frac{1}{5} d u

Take the constant out:

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

= \frac{1}{5} \cdot \int_{0}^{5 π} cos^{4} (u) d u

Simplify

cos^{4} (u) : cos^{3} (u) cos (u)

= \frac{1}{5} \cdot \int_{0}^{5 π} cos^{3} (u) cos (u) d u

Apply Integration By Parts

: [cos^{3} (u) sin (u) - \int - 3 cos^{2} (u) sin^{2} (u) d u]_{0}^{5 π}

= \frac{1}{5} [cos^{3} (u) sin (u) - \int - 3 cos^{2} (u) sin^{2} (u) d u]_{0}^{5 π}

\int - 3 cos^{2} (u) sin^{2} (u) d u = - \frac{3}{8} (u - \frac{1}{4} sin (4 u))

= \frac{1}{5} [cos^{3} (u) sin (u) - (- \frac{3}{8} (u - \frac{1}{4} sin (4 u)))]_{0}^{5 π}

Simplify

\frac{1}{5} [cos^{3} (u) sin (u) - (- \frac{3}{8} (u - \frac{1}{4} sin (4 u)))]_{0}^{5 π} : \frac{1}{5} [\frac{1}{32} (32 cos^{3} (u) sin (u) + 3 (4 u - sin (4 u)))]_{0}^{5 π}

= \frac{1}{5} [\frac{1}{32} (32 cos^{3} (u) sin (u) + 3 (4 u - sin (4 u)))]_{0}^{5 π}

Compute the boundaries:

\frac{15 π}{8}

= \frac{1}{5} \cdot \frac{15 π}{8}

Simplify

= \frac{3 π}{8}

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What is the integral from 0 to pi of cos^4(5x) ?
The integral from 0 to pi of cos^4(5x) is (3pi)/8