Bonjour,
1)
[tex] \frac{5}{3} - 2 = \frac{5}{3} - \frac{6}{3} = \frac{5 - 6}{3} = - \frac{1}{3} [/tex]
2)
[tex] \frac{3}{8} = \frac{3 \times 9}{8 \times 9} = \frac{27}{72} [/tex]
[tex] \frac{4}{9} = \frac{4 \times 8}{9 \times 8} = \frac{32}{72} [/tex]
32/72 > 27/72 donc 4/9 > 3/8
3)
[tex] \frac{2}{5} = \frac{4}{x} [/tex]
[tex]x = 4 \times \frac{5}{2} = \frac{4 \times 5}{2} = \frac{20}{2} = 10[/tex]
4)
[tex] \frac{12}{21} = \frac{3 \times 4}{3 \times 7} = \frac{4}{7} [/tex]
=> Donc 12/21
8/21 => Irréductible
7/14 = (7×1)/(7 × 2) = 1/2 # 4/7
6/9 = 1/3 # 4/7
5)
[tex]a = \frac{3}{7} - \frac{2}{5} [/tex]
[tex] = \frac{3 \times 5}{7 \times 5} - \frac{2 \times 7}{5 \times 7} [/tex]
[tex] = \frac{15}{35} - \frac{14}{35} [/tex]
[tex] = \frac{1}{35} [/tex]
