aider moi s il vous plaît merci d avance

[tex]A= \frac{1}{3} - \frac{1}{3} * \frac{4}{7} = \frac{1}{3} - \frac{1*4}{3*7} = \frac{1}{3} - \frac{4}{21} = \frac{1*21}{3*21} - \frac{4*3}{3*21} = \frac{21}{63} - \frac{12}{63} = \frac{9}{63} = \frac{1}{7} [/tex]

[tex]B=( \frac{5}{4} - \frac{2}{3} )*(3- \frac{9}{7} )=( \frac{5*3}{4*3} - \frac{2*4}{3*4} )*(3- \frac{9}{7} )=( \frac{15}{12} - \frac{8}{12} )*(3- \frac{9}{7} )[/tex]=[tex] \frac{7}{12} *( \frac{3}{1} - \frac{9}{7} )= \frac{7}{12} *( \frac{3*7}{1*7} - \frac{9*1}{7*1} )= \frac{7}{12} *( \frac{21}{7} - \frac{9}{7} )= \frac{7}{12} * \frac{12}{7} = \frac{7*12}{12*7} = \frac{84}{84} [/tex]=1

Voilà