[tex]a = 2 \\ \\ \frac{a}{7} + \frac{1}{7} + \frac{3}{7} = \frac{6}{7} \\ \frac{a + 1 + 3}{7} = \frac{6}{7} \\ \frac{a + 4}{7} = \frac{6}{7} \\ a + 4 = 6 \\ a = 6 - 4 \\ a = 2 \\ verificare \\ \frac{2 + 1 + 3}{7} = \frac{6}{7} \\ \frac{6}{7} = \frac{6}{7} (adevarat)[/tex]
