弓高为H=45cm、半径为R=125cm
弦长L=2*(R^2-(R-H)^2)^0.5
=2*(125^2-(125-45)^2)^0.5
=2*(125^2-80^2)^0.5
=2*96.047
=192.094cm
圆心角A=2*ARC SIN((L/2)/R)
=2*ARC SIN((192.097/2)/125)
=100.416度
弓形的面积S=PI*R^2*A/360-L*(R-H)/2
=PI*125^2*100.416/360-192.094*80/2
=13692.108-7683.76
=6008.348