弦长L=6.1米,弦中心到弧顶H=1.5米,求个弧长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)
=1.5/2+6.1^2/(8*1.5)
=3.851米
A=2*ARC SIN((L/2)/R)
=2*ARC SIN((6.1/2)/3.851)
=104.75度
=104.75*PI/180
=1.828275弧度
C=R*A=3.851*1.828275=7.04米