[TEX]20x + 11y = 1997[/TEX]
[TEX]\Rightarrow y = \frac{1997 - 20x}{11}[/TEX]
[TEX]= \frac{1991 -22x + 6 +2x}{11}[/TEX]
[TEX]= 181 - 2x + \frac{6 + 2x}{11} [/TEX]
đặt [TEX]\frac{6 +2x}{11} = t_1 (t_1 \in Z)[/TEX]
[TEX]\Rightarrow x = \frac{11t_1 - 6 }{2} = 5t_1 - 3 + \frac{t_1}{2}[/TEX]
đặt [TEX]\frac{t_1}{2} = t (t \in Z)[/TEX]
[TEX]\Rightarrow t_1 = 2t[/TEX]
[TEX]\Rightarrow \left{\begin{x = 11t - 3}\\{y = 187 - 20t}[/TEX]