Réponse :
Bonjour,
a)
[tex]\dfrac{4}{3} - ( \dfrac{1}{2} + \dfrac{7}{8} )\\\\= \dfrac{4 \times 8}{3 \times 8} - (\dfrac{1 \times 12}{2 \times 12} + \dfrac{7 \times 3}{8 \times 3} )\\\\= \dfrac{32}{24} - (\dfrac{12}{24} + \dfrac{21}{24})\\\\= \dfrac{32}{24} - \dfrac{33}{24}\\\\= -\dfrac{1}{24}[/tex]
b)
[tex]\dfrac{4}{3} - \dfrac{7}{5} - (\dfrac{3}{5} - \dfrac{5}{7})\\\\= \dfrac{4}{3} - \dfrac{7 \times 7}{5 \times 7} - (\dfrac{3 \times 7}{5 \times 7} - \dfrac{5 \times 5}{7 \times 5})\\\\= \dfrac{4}{3} - \dfrac{49}{35} - (\dfrac{21}{35} - \dfrac{25}{35})\\\\= \dfrac{4}{3} - \dfrac{49}{35} - (-\dfrac{4}{35})\\\\= \dfrac{4}{3} - \dfrac{49}{35} + \dfrac{4}{35}\\\\= \dfrac{4 \times 35}{3 \times 35} - \dfrac{45 \times 3}{35 \times 3}\\\\= \dfrac{140}{105} - \dfrac{135}{105}\\\\= \dfrac{5}{105}\\\\= \dfrac{1}{21}[/tex]
