Verified answer

Explicação passo-a-passo:

[tex]a) \frac{5}{7} - \frac{2}{9} = mmc = 63[/tex]

[tex] \frac{45 - 14}{63} = \frac{21}{63} = \frac{1}{3} [/tex]

[tex]b) \frac{ - 4}{5} - ( - \frac{3}{7} ) = \frac{ - 4}{5} + \frac{3}{7} = mmc = 35[/tex]

[tex] \frac{ - 28 + 15}{35} = \frac{ - 13}{35} [/tex]