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受欢迎的微积分 >

integral of (18)/(1+9x^2)

解答

\int \frac{18}{1 + 9 x ^{2}} d x

解答

6 arctan (3 x) + C

求解步骤

\int \frac{18}{1 + 9 x ^{2}} d x

提出常数:

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

= 18 \cdot \int \frac{1}{1 + 9 x ^{2}} d x

使用换元积分法

= 18 \cdot \int \frac{1}{3 ( 1 + u ^{2} )} d u

提出常数:

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

= 18 \cdot \frac{1}{3} \cdot \int \frac{1}{1 + u ^{2}} d u

使用积分常见定则:

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

= 18 \cdot \frac{1}{3} arctan (u)

u = 3 x

代回

= 18 \cdot \frac{1}{3} arctan (3 x)

化简

18 \cdot \frac{1}{3} arctan (3 x) : 6 arctan (3 x)

= 6 arctan (3 x)

解答补常数

= 6 arctan (3 x) + C

作图

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