β=0,r=3,
β=PI/2,r=0,
β=PI,r=3,
β=3PI/2,r=0,
β=2PI,r=3.
面积=(1/2)S_{0->2PI}dβS_{0->3(1-sinβ)}r^2dr
=(1/6)S_{0->2PI}[3(1-sinβ)]^3dβ
=(9/2)S_{0->2PI}[1-3sinβ+3(sinβ)^2-(sinβ)^3]dβ
=(9/2)S_{0->2PI}[1+3(sinβ)^2]dβ
=(9/2)*(2PI)+(9/2)S_{0->2PI}3[1-cos(2β)]/2dβ
=(9/2)*(2PI)+(9/2)*(3/2)*2PI
=45PI/2