(i) Determine the order of the multistep method

$$\mathbf{y}_{n+2}-(1+\alpha) \mathbf{y}_{n+1}+\alpha \mathbf{y}_{n}=h\left[\frac{1}{12}(5+\alpha) \mathbf{f}_{n+2}+\frac{2}{3}(1-\alpha) \mathbf{f}_{n+1}-\frac{1}{12}(1+5 \alpha) \mathbf{f}_{n}\right]$$

for the solution of ordinary differential equations for different choices of $\alpha$ in the range $-1 \leqslant \alpha \leqslant 1$.

(ii) Prove that no such choice of $\alpha$ results in a method whose linear stability domain includes the interval $(-\infty, 0)$.