✔ 最佳答案
Let A(R,0), B(Rcosx, Rsinx), C(Rcosy, Rsiny), y>x, then
A= (y-x)/2, B=(2pi-y)/2, C=x/2.
S={(x,y)| 0 < x < 2pi, x < y < 2pi}
TA={(x,y)| (x,y) in S, (y-x)/2 > pi/2}
TB={(x,y)| (x,y) in S, (2pi-y)/2 > pi/2}
TC={(x,y)| (x,y) in S, x/2 > pi/2}
p= area(TA union TB union TC)/area(S) = 3/4
圖片參考:
http://imgcld.yimg.com/8/n/HA06881079/o/20140215175102.jpg