cho 3 dãy số $(x_{n}),(y_{n}),(z_{n})$ thỏa mãn $x_{1}=-2,y_{1}=1,z_{1}=-1$
và $\left\{\begin{matrix}x_{n+1}=3x_{n}-6y_{n}-z_{n} \\ y_{n+1}=-x_{n}+2y_{n}+z_{n} \\ z_{n+1}=x_{n}+3y_{n}-2z_{n} \end{matrix}\right.$
Tìm $lim\frac{x_{n}+y_{n}+z_{n}}{2^n+5^n}$
