Aidez moi svp pour cet exercice

Bonjour ;

Exercice n° 3 .

[tex]A=\dfrac{7}{6}+\dfrac{5}{2}\times\dfrac{(-3)}{4}=\dfrac{7}{6}+\dfrac{-15}{8}=\dfrac{7}{6}-\dfrac{15}{8}=\dfrac{28}{24}-\dfrac{45}{24}\\\\\\=\dfrac{28-45}{24}=\dfrac{-17}{24}=-\dfrac{17}{24}\ .[/tex]

[tex]B=\dfrac{21}{4}\div(\dfrac{2}{9} -\dfrac{3}{-4} )=\dfrac{21}{4} \div(\dfrac{2}{9}+\dfrac{3}{4})=\dfrac{21}{4} \div(\dfrac{8}{36} +\dfrac{27}{36})\\\\\\=\dfrac{21}{4} \div\dfrac{35}{36}=\dfrac{21}{4} \times\dfrac{36}{35}=\dfrac{21}{35} \times\dfrac{36}{4}=\dfrac{3}{5}\times9=\dfrac{27}{5}\ .[/tex]