x^2+y^2-4x+6y+13=0
x^2-4x+4+y^2+6y+9=0
(x-2)^2+(y+3)^2=0
x-2=0,y+3=0
x=2,y=-3
(x^2+y)/(x^2-y)=(4-3)/(4+3)=1/7