Răspuns:
[tex] x \in \{21,42,63,84\}[/tex]
Explicație pas cu pas:
x : 17 = y rest 4y, 4y < 17
[tex]4y < 17, y\in \mathbb{N}\Rightarrow y \leq 4 \Rightarrow y < 4\\x = 17\cdot y + 4y = 17y + 4y = \boxed{21y = x}\Rightarrow x \in \{21k, k\in \{1,2,3,4\}\}\Rightarrow x \in\{21,42,63, 84\}[/tex]
