Réponse:
[tex]a = \frac{ - 2}{6} \times \frac{21}{5} \\ = \frac{ - 2 \times 3 \times 7}{2 \times 3 \times 5} \\ = \frac{ - 7}{5} [/tex]
[tex]b = \frac{ - 12}{7} \times \frac{7}{5} \times \frac{5}{6} \\ = \frac{ - 6 \times 2 \times 7 \times 5}{7 \times 5 \times 6 } \\ = - 2[/tex]
[tex]c = \frac{4}{9} \times \frac{3}{7} \times \frac{21}{4} \\ = \frac{4 \times 3 \times 7 \times 3}{3 \times 3 \times 7 \times 4} \\ = 1[/tex]
[tex]d = \frac{8}{5} \times \frac{ - 5}{3} \times \frac{ - 9}{16} \\ = \frac{8 \times 5 \times3 \times 3 }{5 \times 3 \times 8 \times 2} \\ = \frac{3}{2} [/tex]
