$\frac{x}{y}$ $x_{123}$ $x_{123}$ $x_{123}$ $\frac{x}{y}$ $\frac{x}{y}$ $\lim_{n \to \infty} a_n$ \(\left[ \begin{array}{l}x=2\\x=-1\end{array} \right.\) \(\left[ \begin{array}{l}x=2\\x=-1\end{array} \right.\) \(\left[ \begin{array}{l}x=2\\x=-1\end{array} \right.\)