Bonjour,
[tex]A=\frac{2}{7} -\frac{3}{7} *\frac{14}{9} =\frac{2}{7} -\frac{3*14}{7*9} =\frac{2*9}{7*9}-\frac{42}{63} =\frac{18}{63} -\frac{42}{63} = \frac{18-42}{63} =\frac{-24}{63} =-\frac{8}{21} \\\\B=-\frac{7}{8}*(\frac{2}{3}-1)=-\frac{7}{8}*(\frac{2}{3}-\frac{3}{3})=-\frac{7}{8}*\frac{-1}{3} =\frac{7}{24} \\\\C=\frac{4}{5} *\frac{1}{4} +\frac{2}{5} =\frac{4}{5*4} +\frac{2*4}{5*4}=\frac{4}{20}+\frac{8}{20} =\frac{12}{20}[/tex]
