连接圆心和弧上面的一点形成OE,设角EOB为a.
S = R^2[sinacosa-(√3/3)sin^2 a]
=R^2(1/2sin2a+√3/6cos2a-√3/6)
=R^2[√3/3(sin2a+b)-√3/6]
≤√3/6R^2