Quelqu'un pourrais m'auder je ne comprends rien du tout svp merci

Bonsoir Leaanesquintao

[tex]1)\ \dfrac{3}{4}+\dfrac{2}{7}-\dfrac{7}{9}=\dfrac{3\times7\times9}{4\times7\times9}+\dfrac{2\times4\times9}{7\times4\times9}-\dfrac{7\times4\times7}{9\times4\times7}\\\\\\\dfrac{3}{4}+\dfrac{2}{7}-\dfrac{7}{9}=\dfrac{189}{252}+\dfrac{72}{252}-\dfrac{196}{252}\\\\\\\boxed{\dfrac{3}{4}+\dfrac{2}{7}-\dfrac{7}{9}=\dfrac{65}{252}}[/tex]

[tex]2)\ \dfrac{5}{6}+\dfrac{13}{4}+\dfrac{8}{8}-\dfrac{1}{2}\\\\=\dfrac{5}{6}+\dfrac{13}{4}+1-\dfrac{1}{2}\\\\=\dfrac{5\times2}{6\times2}+\dfrac{13\times3}{4\times3}+\dfrac{12}{12}-\dfrac{1\times6}{2\times6}\\\\=\dfrac{10}{12}+\dfrac{39}{12}+\dfrac{12}{12}-\dfrac{6}{12}\\\\=\dfrac{55}{12}\\\\\boxed{\dfrac{5}{6}+\dfrac{13}{4}+\dfrac{8}{8}-\dfrac{1}{2}=\dfrac{55}{12}}[/tex]

[tex]3)\ 0,5+\dfrac{5}{4}=\dfrac{1}{2}+\dfrac{5}{4}\\\\=\dfrac{2}{4}+\dfrac{5}{4}\\\\=\dfrac{7}{4}\\\\\boxed{0,5+\dfrac{5}{4}=\dfrac{7}{4}}[/tex]

[tex]4)\ \dfrac{5}{2}\times\dfrac{3}{4}\times\dfrac{2}{3}= \dfrac{5\times3\times2}{2\times4\times3}\\\\=\dfrac{30}{24}\\\\=\dfrac{5\times6}{4\times6}\\\\=\dfrac{5}{4}\\\\\boxed{\dfrac{5}{2}\times\dfrac{3}{4}\times\dfrac{2}{3}=\dfrac{5}{4}}[/tex]

[tex]5)\ \dfrac{5+2-5}{7}+\dfrac{3+4-1}{12-2}=\dfrac{2}{7}+\dfrac{6}{10}\\\\=\dfrac{2}{7}+\dfrac{3}{5}\\\\=\dfrac{2\times5}{7\times5}+\dfrac{3\times7}{5\times7}\\\\=\dfrac{10}{35}+\dfrac{21}{35}\\\\=\dfrac{31}{35}\\\\\boxed{\dfrac{5+2-5}{7}+\dfrac{3+4-1}{12-2}=\dfrac{31}{35}}[/tex]

[tex]6)\ \dfrac{(-3\times2)+1}{8}\times\dfrac{-6-2}{(3\times4)-6}\\\\=\dfrac{-6+1}{8}\times\dfrac{-8}{12-6}\\\\=\dfrac{-5}{8}\times(\dfrac{-8}{6})\\\\=\dfrac{5}{8}\times\dfrac{8}{6}\\\\=\dfrac{5}{1}\times\dfrac{1}{6}\\\\=\dfrac{5}{6}[/tex]

[tex]\\\\\boxed{\dfrac{(-3\times2)+1}{8}\times\dfrac{-6-2}{(3\times4)-6}=\dfrac{5}{6}}[/tex]

[tex]7)\ +0,5+\dfrac{1}{3}-0,25-\dfrac{2}{6}\\\\=0,5+\dfrac{1}{3}-0,25-\dfrac{1}{3}\\\\=0,5-0,25\\\\=0,50-0,25\\\\=0,25\\\\\boxed{0,5+\dfrac{1}{3}-0,25-\dfrac{2}{6}=0,25}[/tex]