已知拱高是H=0.31米弦长是L=1.155米求弧长C是多少?
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)
=0.31/2+1.155^2/(8*0.31)
=0.6929米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((1.155/2)/0.6929)
=112.9度
C=π*R*A/180=π*0.6929*112.9/180=1.3655米