弦长L=20m,弧高H=3m,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)
=3/2+20^2/(8*3)
=18.167m
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((20/2)/18.167)
=66.797度
=66.797*PI/180
=1.1658弧度
C=A*R
=1.1658*18.167
=21.179m