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) =12.5米A=2*ARC SIN((L/2)/R) =2*ARC SIN((15/2)/12.5) =73.74度 =73.74*PI/180 =1.287弧度C=R*A=12.5*1.687=16.088米
给你方法自己做 画图求半经
