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受欢迎的微积分 >

integral of (x^2)/((64+x^2)^2)

解答

\int \frac{x ^{2}}{( 64 + x ^{2} ) ^{2}} d x

解答

\frac{1}{8} (\frac{1}{2} arctan (\frac{x}{8}) - \frac{4 x}{64 + x ^{2}}) + C

求解步骤

\int \frac{x ^{2}}{( 64 + x ^{2} ) ^{2}} d x

使用换元积分法

= \int \frac{u ^{2}}{8 ( u ^{2} + 1 ) ^{2}} d u

提出常数:

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

= \frac{1}{8} \cdot \int \frac{u ^{2}}{( u ^{2} + 1 ) ^{2}} d u

将

\frac{u ^{2}}{( u ^{2} + 1 ) ^{2}}

用部份分式展开:

\frac{1}{u ^{2} + 1} - \frac{1}{( u ^{2} + 1 ) ^{2}}

= \frac{1}{8} \cdot \int \frac{1}{u ^{2} + 1} - \frac{1}{( u ^{2} + 1 ) ^{2}} d u

使用积分加法定则:

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

= \frac{1}{8} (\int \frac{1}{u ^{2} + 1} d u - \int \frac{1}{( u ^{2} + 1 ) ^{2}} d u)

\int \frac{1}{u ^{2} + 1} d u = arctan (u)

\int \frac{1}{( u ^{2} + 1 ) ^{2}} d u = \frac{1}{2} (arctan (u) + \frac{u}{1 + u ^{2}})

= \frac{1}{8} (arctan (u) - \frac{1}{2} (arctan (u) + \frac{u}{1 + u ^{2}}))

u = \frac{x}{8}

代回

= \frac{1}{8} (arctan (\frac{x}{8}) - \frac{1}{2} (arctan (\frac{x}{8}) + \frac{\frac{x}{8}}{1 + ( \frac{x}{8} ) ^{2}}))

化简

\frac{1}{8} (arctan (\frac{x}{8}) - \frac{1}{2} (arctan (\frac{x}{8}) + \frac{\frac{x}{8}}{1 + ( \frac{x}{8} ) ^{2}})) : \frac{1}{8} (\frac{1}{2} arctan (\frac{x}{8}) - \frac{4 x}{64 + x ^{2}})

= \frac{1}{8} (\frac{1}{2} arctan (\frac{x}{8}) - \frac{4 x}{64 + x ^{2}})

解答补常数

= \frac{1}{8} (\frac{1}{2} arctan (\frac{x}{8}) - \frac{4 x}{64 + x ^{2}}) + C

作图

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