Réponse :
[tex]\frac{5}{2} +\frac{2}{8} =\frac{5 \times 4}{2 \times 4} + \frac{2}{8} =\frac{20}{8}+\frac{2}{8}=\frac{22}{8} = \frac{11}{4} \\\frac{4}{2} + 5 = 2 + 5 = 7\\\frac{2}{9} + \frac{3}{2} = \frac{2 \times 2}{9 \times 2} + \frac{3 \times 9}{2 \times 9} = \frac{4}{18} + \frac{27}{18} = \frac{31}{18}[/tex]
[tex]2 + \frac{5}{3} = \frac{2}{1} +\frac{5}{3} =\frac{2 \times 3}{1 \times 3} +\frac{5}{3} = \frac{6}{3} + \frac{5}{3} = \frac{11}{3} \\\frac{3}{7} + \frac{4}{14} = \frac{3}{7} + \frac{2 \times 2}{7 \times 2} = \frac{3}{7} + \frac{2}{7} = \frac{5}{7} \\\frac{1}{2} -\frac{1}{3} =\frac{1 \times 3}{2 \times 3} -\frac{1 \times 2}{3 \times 2} = \frac{3}{6} - \frac{2}{6} = \frac{1}{6}[/tex]
[tex]2- \frac{1}{8} = \frac{2}{1} - \frac{1}{8} = \frac{2 \times 8 }{1 \times 8} - \frac{1}{8} = \frac{16 }{8} - \frac{1}{8} = \frac{15}{8} \\\frac{5}{6} - \frac{2}{3} = \frac{5}{6} - \frac{2 \times 2}{3 \times 2} = \frac{5}{6} - \frac{4}{6} = \frac{1}{6}\\\frac{2}{7} - \frac{3}{4} = \frac{2 \times 4}{7 \times 4} - \frac{3 \times 7}{4 \times 7} = \frac{8}{28} - \frac{21}{28} = - \frac{13}{28}\\[/tex]
[tex]\frac{4}{3} - \frac{4}{7} = \frac{4 \times 7}{3 \times 7} - \frac{4 \times 3}{7 \times 3} = \frac{28}{21} - \frac{12}{21} = - \frac{16}{21}\\[/tex]
Voilà !
