[tex]Bonjour;\\\\\\A=\dfrac{3}{4}+\dfrac{1}{2}\times\dfrac{2}{3}-1=\dfrac{3}{4}+\dfrac{2}{2}\times\dfrac{1}{3}-1=\dfrac{3}{4}+\dfrac{1}{3}-1\\\\\\=\dfrac{3\times3}{4\times3}+\dfrac{1\times4}{3\times4}-\dfrac{12}{12}=\dfrac{9}{12}+\dfrac{4}{12}-\dfrac{12}{12}=\dfrac{9+4-12}{12}=\dfrac{1}{12}\ .\\\\\\\\B=\dfrac{15}{14}-\dfrac{6}{7}\times\dfrac{2}{3}=\dfrac{15}{14}-\dfrac{6}{3}\times\dfrac{2}{7}=\dfrac{15}{14}-2\times\dfrac{2}{7}=\dfrac{15}{14}-\dfrac{4}{7}\\\\\\[/tex]
[tex]=\dfrac{15}{14}-\dfrac{4\times2}{7\times2}=\dfrac{15}{14}-\dfrac{8}{14}=\dfrac{7}{14}=\dfrac{1}{2}\ .[/tex]
