弦長(zhǎng)為L(zhǎng)=4.9米,弓形高為H=0.7米,求弧長(zhǎng)C?
弧半徑為R,弧所對(duì)的圓心角為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)
=0.7/2+4.9^2/(8*0.7)
=4.6375米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((4.9/2)/4.6375)
=63.78度
C=PI*R*A/180=PI*4.6375*63.78/180=5.162米