Réponse:
[tex] \frac{3}{7} \div \frac{4}{5} = \frac{3}{7} \times \frac{5}{4} = \frac{3 \times 5}{7 \times 4} = \frac{15}{28} \\ 4 \div \frac{7}{9} = 4 \times \frac{9}{7} = \frac{4 \times 9}{7} = \frac{36}{7} [/tex]
[tex] \frac{a}{b} \div \frac{c}{d} = \frac{a}{b} \times \frac{d}{c} [/tex]