Răspuns:
[tex]\frac{9}{10} =\frac{5}{10} +a= > a=\frac{9}{10} -\frac{5}{10} = > a=\frac{4}{5} \\\\\frac{6}{7} =a+\frac{1}{7} = > \frac{6}{7} -\frac{1}{7} =a= > a=\frac{5}{7} \\\\\frac{8}{9} =\frac{2}{9} +a= > \frac{8}{9} -\frac{2}{9} =a= > a=\frac{6}{9} \\\\\frac{2}{2} =\frac{1}{2} +\frac{1}{2}[/tex]
