B
bat.nap.quan.tai.hon.em.lan.cuoi
2.[tex]\left\{\begin{matrix}y^2=(5x+4)(4-x)\\ y^2-5x^2-4xy+16x-8y+16=0\end{matrix}\right.[/tex]
3.[tex]\left\{\begin{matrix}4xy+4(x^2+y^2)+\frac{3}{(x+y)^2}=7\\ 2x+\frac{1}{x+y}=3\end{matrix}\right.[/tex]
[tex]\left\{\begin{matrix}y^2=(5x+4)(4-x)\\ y^2-5x^2-4xy+16x-8y+16=0\end{matrix}\right [/tex][tex]\Leftrightarrow \left\{\begin{matrix}y^2=(5x+4)(4-x)\\ (y-5x-4)(y+x-4)=0\end{matrix}\right.[/tex]
[TEX]\left\{\begin{matrix}4xy+4(x^2+y^2)+\frac{3}{(x+y)^2}=7\\ 2x+\frac{1}{x+y}=3\end{matrix}\right [/tex][tex]\Leftrightarrow \left\{\begin{matrix}3(a+\frac{1}{a})^2+b^2=13\\ a+\frac{1}{a}+b=3\end{matrix}\right[/TEX]
[TEX](a=x+y; b=x-y)[/TEX]
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