设p(cost,sint) t∈(-∏,∏)
M为(x,y)
x=cost+(3-cost)*(2/3)
y=(1/3)*sint
化简得x=2+(1/3)cost
y=(1/3)sint
y∈[-1/3,1/3 ]
最后整理 (x-2)^2+y^2=1/9