已知弦长L=11,弦高H=1.8,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)
=1.8/2+11^2/(8*1.8)
=9.303
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((11/2)/9.303)
=72.487度
C=PI*R*A/180=PI*9.303*72.487/180=11.769