【基础微积分】he area of the region enclosed by the polar curve r=1

面积S＝1/2∫(0到2π) r^2 dθ＝1/2∫(0到2π) (1-cosθ)^2 dθ＝1/2∫(0到2π) (1-2cosθ+(cosθ)^2) dθ＝1/2∫(0到2π) (1-2cosθ+1/2+1/2cos2θ) dθ＝3π/2