x²+4x+y²+6y+13=0
x²+4x+4+y²+6y+9=0
(x+2)²+(y+3)²=0
(x+2)²=0,(y+3)²=0
x=-2,y=-3
(x-2y)/(x²+y²)
=[-2-2*(-3)]/[(-2)^2+(-3)^2]
=(-2+6)/(4+9)
=4/13