Question

[Nguyen Phuc Duy]

Giải các hệ phương trình :

a ) \(\hept{\begin{cases}x^2-3y=2\\9y^2-8x=8\end{cases}}\)

b ) \(\hept{\begin{cases}xy+x+y=3\\\frac{1}{x^2+2x}+\frac{1}{y^2+2y}=\frac{2}{3}\end{cases}}\)

Answer 1

[Agatsuma Zenitsu]

\(a,\hept{\begin{cases}x^2-3y=2\\9y^2-8x=8\end{cases}}\)

\(x^2-3y=2\)

\(y=\frac{1^2-2}{3}\)

\(9-\left(\frac{x^2-2}{3}\right)^2-8x=8\)

\(\Rightarrow x^4-4x^2+4-8x-8=0\)

\(\Rightarrow x^4-4x^2-8x-4=0\)

\(\Rightarrow\left(x^2-2x-2\right)\left(x^2+2x+2\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=1+\sqrt{3}\\x=1-\sqrt{3}\end{cases}}\Leftrightarrow\orbr{\begin{cases}y=\frac{2+2\sqrt{3}}{3}\\y=\frac{2-2\sqrt{3}}{3}\end{cases}}\)

Vậy ................................