P1=P2=P3=P4=P1是一块半径为1的半圆形纸板,在P1的坐下端剪去一个半径为1/2的半圆后,得到图形P2,然后依

s1=π * 1*1*0.5；
s2=π * 1*1*0.5-π * (1/2)*(1/2)*0.5=s1-π * (1/2)*(1/2)*0.5;
s3=π * 1*1*0.5-π * (1/2)*(1/2)*0.5-π * (1/2/2)*(1/2/2)*0.5=s2-π * (1/2/2)*(1/2/2)*0.5;
同理：
sn=sn-1-π *(1/2/2…/2）*(1/2/2…/2）*0.5 共除n-1个二；
即
sn-sn-1=-π *(1/2/2…/2）*(1/2/2…/2）*0.5 共除n-1个二；