设圆半径为r,则
(r-0.3)^2+2^2=r^2
即r^2-0.6r+0.09+4=r^2所以r=4.09/0.6=6.81667米
圆心角=2arctg(2/6.51667)
弧长=2r*arctg(2/6.51667)=4.0597米