Explicație pas cu pas:
[tex](1000a + 100b + 10a + a) + (10b + a) + 11a = 2021 \\ [/tex]
[tex]1022a + 111b = 2021[/tex]
[tex]1022a + 111b - 2021 = 0[/tex]
[tex](9 \times 111 + 23)a + 111b - (18 \times 111 + 23) = 0[/tex]
=>
[tex]111(9a + b - 18) + 23(a - 1) = 0[/tex]
=>
[tex]\left \{ {{9a + b - 18 = 0} \atop {a - 1 = 0}} \right. \\ = > \left \{ {{b = 1} \atop {a = 1}} \right. \\ [/tex]
