弦长L=4.8米，拱高H=0.7米，弧长C多少 ?弧半径为R，弧所对的圆心角为A。R=H/2+L^2/(8*H)=0.7/2+4.8^2/(8*0.7) =4.46429米A=2*ARC COS((R-H)/R) =2*ARC COS((4.46429-0.7)/4.46429) =65.04度C=π*R*A/180=π*4.46429*65.04/180=5.06775米
