L-am făcut doar pe a)
[tex]\Big(\overline{ab}^2\Big)-\Big(\overline{ba}^2\Big) = (\overline{ab} - \overline{ba})( \overline{ab} +\overline{ba}) = \\ \\ = \Big[10a+b - (10b+a)\Big]\Big[10a+b +(10b+a)\Big] = \\ \\ = (9a-9b)(11a+11b) = 9\cdot 11\cdot(a-b)(a+b)\,\, \vdots\,\, 9[/tex]
