已知弦长L=17.4米弦高H=2.5米求弧长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*H*R+H^2+L^2/4
2*H*R=H^2+L^2/4
R=H/2+L^2/(8*H)
=2.5/2+17.4^2/(8*2.5)
=16.388米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((17.4/2)/16.388)
=64.129度
C=PI*R*A/180=PI*16.388*64.129/180=18.343米