integral from 0 to (3pi)/4 of x^3sin(2x)

解

\int_{0}^{\frac{3 π}{4}} x^{3} sin (2 x) d x

\frac{3 ( - 9 π ^{2} + 8 )}{64}

十進法表記

- 3.78873 \dots

解答ステップ

\int_{0}^{\frac{3 π}{4}} x^{3} sin (2 x) d x

部分積分を適用する

= [\frac{1}{2} (- x^{3} cos (2 x) - 2 \cdot \int - \frac{3}{2} x^{2} cos (2 x) d x)]_{0}^{\frac{3 π}{4}}

\int - \frac{3}{2} x^{2} cos (2 x) d x = - \frac{3}{8} (2 x^{2} sin (2 x) + 2 x cos (2 x) - sin (2 x))

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

簡素化

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

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

限度を計算する:

\frac{3 ( - 9 π ^{2} + 8 )}{64}

= \frac{3 ( - 9 π ^{2} + 8 )}{64}