已知弦长为L,它所对的圆周角为A=120°,则它所对的弧长C为多少?
弧半径为R.
R=(L/2)/(SIN(A/2))
=(L/2)/(SIN(120°/2))
=(L/2)/(SIN(60°))
=0.433013*L
A=120°=120°*PI/180°=2.094395弧度
C=A*R=2.094395*0.433013*L=0.9069*L