已知弦长L=18m及高度H=3m求弧长C?
弧半径为R,弧所对的圆心角为A
R=H/2+L^2/(8*H)
=3/2+18^2/(8*3)
=15米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((18/2)/15)
=73.74度
=73.74*PI/180
=1.287弧度
C=A*R
=1.287*15
=19.305米
弧长C=19.305米.