弦长L=28.6,弦中心到弧顶H=1.2,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)
=1.2/2+28.6^2/(8*1.2)
=97.976
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((28.6/2)/97.976)
=16.785度
=16.785*PI/180
=0.29295弧度
C=A*R=0.29295*97.976=28.703