弦长L=15米拱高H=2.5米弧长C是多少米?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)=2.5/2+15^2/(8*2.5)=12.5A=2*ARC SIN((L/2)/R)=2*ARC SIN((15/2)/12....