M(x,y)若M分向量PQ的比1:2λ=1/2定点Q(4,0)P(x1,y1)x=(x1+1/2*4)/(1+1/2)x1=3/2x-2y=(y1+0)/(1+1/2)=y1=3/2y知p点为圆x^2+y^2=4(3/2x-2)^2+(3/2y)^2=4M的轨迹方程:x^2+y^2+8/3=0