a, x2 -2xy+3y2 -4y+2=0
\(\Leftrightarrow\)(x2-2xy+y2)+(y2-2y+1)+(y2-2y+1)=0
\(\Leftrightarrow\) (x-y)2+(y-1)2+(y-1)2=0
\(\Leftrightarrow\) \(\left\{{}\begin{matrix}\left(x-y\right)^2=0\\\left(y-1\right)^2=0\\\left(y-1\right)^2=0\end{matrix}\right.\) \(\Leftrightarrow\) \(\left\{{}\begin{matrix}x=y\\y=1\end{matrix}\right.\)\(\Leftrightarrow\) x=y=1
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