Giải hệ phương trình
1) $\left\{\begin{matrix}x+y+\frac{1}{x}+\frac{1}{y}=5 & \\ x^3+y^3+\frac{1}{x^3}+\frac{1}{y^3}=20 & \end{matrix}\right.$
2) ${\left\{\begin{matrix}x+y+\frac{x}{y}+\frac{y}{x}=4 & \\ x+y+\frac{x^2}{y}+\frac{y^2}{x}=4 & \end{matrix}\right.}{}$
3) $\left\{\begin{matrix}x^2+y^2+4xy=6 & \\ x^2y^2+4(x+y)=9 & \end{matrix}\right.$
4) $\left\{\begin{matrix}x+y+\frac{1}{y}+\frac{1}{x}=9/2 & \\ xy+ 1/xy = 5/2 & \end{matrix}\right.$
5) $\left\{\begin{matrix}xy+\frac{1}{xy}+\frac{x}{y}+\frac{y}{x}=13 & \\ xy-\frac{1}{xy}-\frac{x}{y}+\frac{y}{x}=12 & \end{matrix}\right.$
6) $\left\{\begin{matrix}2x+y=\frac{3}{x^2} & \\ 2y+x=\frac{3}{y^2} & \end{matrix}\right.$
7) $\left\{\begin{matrix}x^3+1=2(x^2-x+y) & \\ y^3+1=2(y^2-y+x) & \end{matrix}\right.$
8) $\left\{\begin{matrix}4x^2+2xy=3 & \\ y^2+2xy=-2 & \end{matrix}\right.$
9) $\left\{\begin{matrix}14x^2-21y^2+22x-39y=0 & \\ 35x^2+28y^2+111x-10y=0 & \end{matrix}\right.$