弦长L=50.4米中间高H=1.81米,算弧长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)
=1.81/2+50.4^2/(8*1.81)
=176.33米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((50.4/2)/176.33)
=16.433度
=16.433*PI/180
=0.286809弧度
C=R*A=176.33*0.286809=50.573米