已知玄长是L=26米,弧顶到玄的距离是H=4.68米,求弧长C?
弧半径为R,弧所对的圆心角为A.
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)
=4.68/2+26^2/(8*4.68)
=20.3956米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((26/2)/20.3965)
=79.196度
C=π*R*A/180=π*20.3956*79.196/180=28.1912米