13 Calculati:
a:
[tex]( \frac{1}{7} + \frac{7}{11} + \frac{2010}{2011}) + ( \frac{6}{7} + \frac{4}{11} - \frac{2010}{2011} )[/tex]
b:
[tex]( \frac{5}{3} + \frac{7}{5} + \frac{9}{7} ) - ( \frac{2}{3} + \frac{2}{5} + \frac{2}{7} )[/tex]
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