知道弦长L=13 和拱高H=2.17 怎么算弧长,弧长C是多少弧半径为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)=2.17/2+13^2/(8*2.17)=10.82A=2*ARC SIN((L/2)/R)=2*AR...