弦长L=355厘米,高H=18厘米,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)
=18/2+355^2/(8*18)
=844.174厘米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((355/2)/844.174)
=23.162度
C=PI*R*A/180=PI*844.174*23.162/180=357.43厘米