已知弦长L=3.5米和拱高是H=0.5米，求半径R怎么求？ R^2=(R-H)^2+(L/2)^2 R^2=R^2-2*R*H+H^2+L^2/4 2*R*H=H^2+L^2/4 R=H/2+L^2/(8*H) =0.5/2+3.5^2/(8*0.5) =3.3125米
