已知弦长3.2米,弦高0.4米求弧长是多少,急,

已知弦长L=3.2米,弦高H=0.4米求弧长C是多少?
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+3.2^2/(8*0.4)
=3.4米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((3.2/2)/3.4)
=56.145度
=56.145*PI/180
=0.97991弧度
C=A*R
=0.97991*3.4
=3.332米