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受欢迎的微积分 >

integral from 2 to 4 of sqrt(4x-x^2)

解答

\int_{2}^{4} 4 x - x^{2} d x

解答

π

+1

十进制

3.14159 \dots

求解步骤

\int_{2}^{4} 4 x - x^{2} d x

对

4 x - x^{2}

配方:

- (x - 2)^{2} + 4

= \int_{2}^{4} - (x - 2)^{2} + 4 d x

使用换元积分法

= \int_{0}^{2} - u^{2} + 4 d u

使用三角换元法

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

提出常数:

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

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

使用三角恒等式改写

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

提出常数:

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

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

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

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

\int_{0}^{\frac{π}{2}} 1 d v = \frac{π}{2}

\int_{0}^{\frac{π}{2}} cos (2 v) d v = 0

= 4 \cdot \frac{1}{2} (\frac{π}{2} + 0)

化简

4 \cdot \frac{1}{2} (\frac{π}{2} + 0) : π

= π

作图

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