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受欢迎的微积分 >

integral from 0 to pi of cos^4(2t)

解答

\int_{0}^{π} cos^{4} (2 t) d t

解答

\frac{3 π}{8}

+1

十进制

1.17809 \dots

求解步骤

\int_{0}^{π} cos^{4} (2 t) d t

使用换元积分法

= \int_{0}^{2 π} cos^{4} (u) \frac{1}{2} d u

提出常数:

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

= \frac{1}{2} \cdot \int_{0}^{2 π} cos^{4} (u) d u

化简

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

= \frac{1}{2} \cdot \int_{0}^{2 π} cos^{3} (u) cos (u) d u

使用分布积分法

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

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

= \frac{1}{2} [cos^{3} (u) sin (u) - (- \frac{3}{8} (u - \frac{1}{4} sin (4 u)))]_{0}^{2 π}

化简

\frac{1}{2} [cos^{3} (u) sin (u) - (- \frac{3}{8} (u - \frac{1}{4} sin (4 u)))]_{0}^{2 π} : \frac{1}{2} [\frac{1}{32} (32 cos^{3} (u) sin (u) + 3 (4 u - sin (4 u)))]_{0}^{2 π}

= \frac{1}{2} [\frac{1}{32} (32 cos^{3} (u) sin (u) + 3 (4 u - sin (4 u)))]_{0}^{2 π}

带入上下限计算后得:

\frac{3 π}{4}

= \frac{1}{2} \cdot \frac{3 π}{4}

化简

= \frac{3 π}{8}

作图

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