要知道圆R(假设半径为r)是否面积比半圆Q(假设面积为q)面积小,其实就是比较r^2 and 1/2q^2 , that is, if (r^2) : (1/2q^2)<1, or (r/q)^2<1/2, or (r/q)<1/1.414,then the condition is sufficient.
1st: r/q<1, in sufficient
2nd: 2pi*r<(pi+2)q, so r/q<(pi+2)/2pi=5.14/6.28, 而5.14/6.28约等于1/1.22 insufficient