求弧长已知弦长3.6米弧高是0.4米

弦长L=3.6,弦中心到弧顶H=0.4,求弧长C?
弧半径为R,弧所对的圆心角为A.
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)
=0.4/2+3.6^2/(8*0.4)
=4.25米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((3.6/2)/4.25)
=50.115度
=50.115*PI/180
=0.874676弧度
C=A*R=0.874676*4.25=3.717米