已知弦长L=3010cm,拱高H=475cm,不知道圆心角A,求弧长C?
弧半径诶R.
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)
=475/2+3010^2/(8*475)
=2621.74cm
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((3010/2)/2621.74)
=70.066度
C=π*R*A/180=π*2621.74*70.066/180=3206.07cm