x²+y²+4x+2y+5=0
(x²+4x+4)+(y²+2y+1)=0
(x+2)²+(y+1)²=0
x+2=0,y+1=0
x=-2,y=-1
根号下(y/x)+根号下(x/y)
=√½+√2
=3√2/2