\(\left\{{}\begin{matrix}x^2-xy+y^2=1\\x^2+2xy-y^2-3x-y=-2\end{matrix}\right.\Leftrightarrow3x^2+y^2-3x-y=0\Leftrightarrow3x^2+y^2=3x+y\Leftrightarrow2x^2=3x+y-xy-1\Leftrightarrow2\left(x-1\right)\left(x+1\right)=\left(1-x\right)\left(y-3\right)\left(xet:x=1\text{ trước}\right)\Leftrightarrow-2x+1=y\Rightarrow x^2-x\left(-2x+1\right)+\left(-2x+1\right)^2=x^2+2x^2-x+4x^2-4x+1=1\Leftrightarrow7x^2-5x=0\Leftrightarrow......\)