`5x^2+2xy+y^2-4x=0`
`<=>(x^2+2xy+y^2)+(4x^2-4x+1)=1`
`<=>(x+y)^2 + (2x-1)^2=1`
Do `(x+y)^2>=0 \forall x in RR`
`(2x-1)>=0 \forall x in RR`
`=>`\(\left[ \begin{array}{l}(x+y)^2=0\\(2x-1)^2=1\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}y=-1\\\ \begin{array}{l}x=0(Loại)\\x=1\end{array} \end{array} \right.\)
\(\left[ \begin{array}{l}(x+y)^2=1\\(2x-1)^2=0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}(x+y)^2=1\\(2x-1)^2=0\end{array} \right.\)
`=>x=1/2` (Loại)
