弦长L=5米拱高H=0.3米怎样求弧长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)
=0.3/2+5^2/(8*0.3)
=10.567米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((5/2)/10.567)
=27.371度
C=PI*R*A/180=PI*10.567*27.371/180=5.048米