设:所求弧所对圆心角为2a,弦长为2l,圆的半径为rr²=(r-20)²+(587/2)²===>r=2163.56sina=l/r=293.5/2163.56=0.1357===>a=7.80º===>2a=15.6º弧长=2*3.14*2163.56*15.6/360=588.78...