integral from 0 to 1 of 2arctan(x^2)

解答

\int_{0}^{1} 2 arctan (x^{2}) d x

\frac{π - 2 ( 2 arctan ( 1 + 2 ) + 2 arctan ( 2 - 1 ) + ln ( 3 - 2 2 ) )}{2}

十进制

0.59580 \dots

求解步骤

\int_{0}^{1} 2 arctan (x^{2}) d x

提出常数:

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

= 2 \cdot \int_{0}^{1} arctan (x^{2}) d x

使用分布积分法

= 2 [x arctan (x^{2}) - \int \frac{2 x ^{2}}{x ^{4} + 1} d x]_{0}^{1}

\int \frac{2 x ^{2}}{x ^{4} + 1} d x = 2 (- \frac{1}{4 2} (ln 2 x^{2} + 22 x + 2 - 2 arctan (2 x + 1)) + \frac{1}{4 2} (ln 2 x^{2} - 22 x + 2 + 2 arctan (2 x - 1)))

= 2 [x arctan (x^{2}) - 2 (- \frac{1}{4 2} (ln 2 x^{2} + 22 x + 2 - 2 arctan (2 x + 1)) + \frac{1}{4 2} (ln 2 x^{2} - 22 x + 2 + 2 arctan (2 x - 1)))]_{0}^{1}

带入上下限计算后得:

\frac{π - 2 ( 2 arctan ( 1 + 2 ) + 2 arctan ( 2 - 1 ) + ln ( 3 - 2 2 ) )}{4}

= 2 \cdot \frac{π - 2 ( 2 arctan ( 1 + 2 ) + 2 arctan ( 2 - 1 ) + ln ( 3 - 2 2 ) )}{4}

化简

= \frac{π - 2 ( 2 arctan ( 1 + 2 ) + 2 arctan ( 2 - 1 ) + ln ( 3 - 2 2 ) )}{2}

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