P(x,y)
到原点的距离是d^2=x^2+y^2=13;
即
x^2+（6/x）^2=13；
x^4+36=13x^2;
x^4-13x^2+36=0;
(x^2-4)*(x^2-9)=0;
x^2=4;或x^2=9;
x=+-2;或者x=+-3;
p(2,3)(-2,-3);(-3,-2);(3,2)