已知弦长为L=4.2米,弦高H=1米,求弧长C?弧半径为R,圆心角为A.R^2=(R-H)^2+(L/2)^2R^2=R^2-2*R*H+H^2+L^2/42*R*H=H^2+L^2/4R=H/2+L^2/(8*H)=1/2+4.2^2/(8*1)=2.601米A=2*ARC SIN((L/2)/R)=2*ARC SIN((4.2/2)/2.601)=10...