已知弓高H=165,弦长L=2220求周长?
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)
=165/2+2220^2/(8*165)
=3816.14
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((2220/2)/3816.14)
=33.82度
=33.82*PI/180
=0.590272弧度
扇形周长=R*2+R*A=3816.14*2+3816.14*0.590272=9884.83