已知跨度L=10米,拱高H=1.3米,求主拱弧长C?弧半径为R,弧所对的圆心角为A.R^2=(R-H)^2+(L/2)^2R^2=R^2-2*R*H+H^2+L^2/42*R*H=H^2+L^2/4R=H/2+L^2/(8*H)=1.3/2+10^2/(8*1.3)=10.2654米A=2*ARCSIN((L/2)/R)=2*ARCSIN((10/2)/10.2654)=58.297度C=π*R*A/180=π*10.2654*58.297/180=10.4447米