Chap9 多元函数积分学 ¶

\[\iint_D f(x,y)\mathrm{d}\sigma=\int_{\alpha}^\beta \mathrm{d}\theta\int_{\varphi_1(\theta)}^{\varphi_2(\theta)}f(r\cos\theta,r\sin\theta)r\mathrm{d}\theta\]