Question

Demonstrați ca oricare ar fi cifra x, nr xx+xxx+xxxx :137

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Answer 1

11x+111x+1111x=1233x=9*137*x, divizibil cu 137
as simple as that!

Answer 2

$\it \overline{xx} +\overline{xxx} +\overline{xxxx} =11x+111x+1111x=1233x=137\cdot9x\in M_{137}$