L=4米,H=0.4米.
弧半径为R,圆心角为A,弧长为C.
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+4^2/(8*0.4)
=5.2米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((4/2)/5.2)
=45.24度
=45.24*PI/180
=0.78958弧度
C=A*R
=0.78958*5.2
=4.106米