∫−22(sin⁡x+4−x2)dx=()∫_{-2}^{2}(\sin x+\sqrt{4-x^{2}}){\rm d}x=(\quad)
A. 44
B. 2π2π
C. 4+2π4+2π
D. 88

Worked solution

1. 将定积分拆分为两项简单的积分

根据定积分的线性性质,将原式拆开为两部分:
∫−22(sin⁡x+4−x2) dx=∫−22sin⁡x dx+∫−224−x2 dx\int_{-2}^{2} (\sin x + \sqrt{4-x^2}) \, \mathrm{d}x = \int_{-2}^{2} \sin x \, \mathrm{d}x + \int_{-2}^{2} \sqrt{4-x^2} \, \mathrm{d}x

2. 利用函数奇偶性求解第一项积分

因为 f(x)=sin⁡xf(x) = \sin x 为奇函数,且积分区间 [−2,2][-2, 2] 关于原点对称,根据对称区间上奇函数积分的性质:
∫−22sin⁡x dx=0\int_{-2}^{2} \sin x \, \mathrm{d}x = 0

3. 利用图形几何意义求解第二项积分并得最终结果

函数 y=4−x2y = \sqrt{4-x^2}(其中 y⩾0y \geqslant 0)表示圆 x2+y2=4x^2 + y^2 = 4 位于 xx 轴及以上的上半圆,半径为 r=2r = 2。
因此定积分 ∫−224−x2 dx\int_{-2}^{2} \sqrt{4-x^2} \, \mathrm{d}x 的几何意义即为该半圆的面积:
∫−224−x2 dx=12πr2=12π(22)=2π\int_{-2}^{2} \sqrt{4-x^2} \, \mathrm{d}x = \frac{1}{2} \pi r^2 = \frac{1}{2} \pi (2^2) = 2\pi

综上所述,原式 =0+2π=2π= 0 + 2\pi = 2\pi。

故正确选项为 B。

Answer

B

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