弓形求弧长 已知弦长L=100 高度是H=4 求弧长C?
弧半径为R,弧所对的圆心角为A.
R^2=(R-H)^2+(L/2)^2
R^2=R^2-2*R*H+H^2+L^2/4
2*R*H=H^2+L^2/4
R=H/2+L^2/(8*H)
=4/2+100^2/(8*4)
=314.5
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((100/2)/314.5)
=18.296度
=18.296*PI/180
=0.31932弧度
C=R*A=314.5*0.31932=100.426