弦长L=17 拱高H=1.8 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)^2R^2=R^2-2*H*R+H^2+L^2/42*H*R=H^2+L^2/4R=H/2+L^2/(8*H)=1.8/2+17^2/(8*1.8)=20.969A=2*ARC SIN((L/2)/R)=2*ARC SIN((17/2)/20.969)=4...