x^2 +5y^2 +2xy+4y+1=0
（x^2+2xy+y^2)+(4y^2+4y+1)=0
(x+y)^2+(2y+1)^2=0
x+y=0
2y+1=0
x=1/2
y=-1/2
则2x+3y=-1/2