已知弓形弦長L=198,高H=48,求弧長C?
弧半徑為R,弧所對的圓心角為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)
=48/2+198^2/(8*48)
=126.094
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((198/2)/126.094)
=103.465度
=103.465*PI/180
=1.805812弧度
C=R*A=126.094*1.805812=227.7