已知弦长L和弦高H,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)
A=(2*ARC SIN((L/2)/R))*PI/180
C=A*R
=(2*ARC SIN((L/2)/R))*PI/180*(H/2+L^2/(8*H))