极坐标曲线所围面积介绍

设$R$R为极坐标曲线包围的区域：$r(\theta)=2-2\cos(\theta)$r, left parenthesis, theta, right parenthesis, equals, 2, minus, 2, cosine, left parenthesis, theta, right parenthesis，$\dfrac{2\pi}{3}\leq \theta\leq \pi$start fraction, 2, pi, divided by, 3, end fraction, is less than or equal to, theta, is less than or equal to, pi。

阴影部分的