(3.8/2)²+(r-0.33)²=r²1.9²+0.33²-2*0.33r=0r=(1.9²+0.33²)/0.66=5.635θ=2arctan1.9/(5.635-0.33)=39.41°弧长=3.14*5.635*2*39.41/360=3.87米
