\hsize 0pt\vsize 0pt\nopagenumbers\overfullrule 0pt\noindent$$\eqalign {y(n) = &\alpha x(n) + \beta(1 + \alpha)x(n - 1) + x(n - 2)\cr- &\beta(1 + \alpha)y(n - 1)  - \alpha y(n - 2)}$$\bye