已知长度L=1.8米，高度H=0.8米求弧长C？弧半径为R，弧所对的圆心角为A。R=H/2+L^2/(8*H)=0.8/2+1.8^2/(8*0.8)=0.90625米A=2*ARC COS((R-H)/R)=2*ARC COS((0.90625-0.8)/0.90625)=166.534度C=π*R*A/180=π*0.90625*166.534/180=2.6341米
