矩形区域也化极坐标来做?你们的题也够无聊的,哈哈.
原式=∫[0-->π/4] dθ∫[0-->1/cosθ] f(rcosθ,rsinθ)r dr + ∫[π/4-->π/2] dθ∫[0-->1/sinθ] f(rcosθ,rsinθ)r d