a.Comparer 20/27 et 7/9 après avoir écrit 7/9 sous la forme .../27. b. Comparer 3/5 et 11/15

Bonsoir

[tex]a.\ \dfrac{20}{27}-\dfrac{7}{9}=\dfrac{20}{27}-\dfrac{3\times7}{3\times9}\\\\\dfrac{20}{27}-\dfrac{7}{9}=\dfrac{20}{27}-\dfrac{21}{27}\\\\\dfrac{20}{27}-\dfrac{7}{9}=-\dfrac{1}{27}\\\\\dfrac{20}{27}-\dfrac{7}{9}<0\\\\\dfrac{20}{27}<\dfrac{7}{9} [/tex]

[tex]b.\ \dfrac{3}{5}-\dfrac{11}{15}=\dfrac{3\times3}{3\times5}-\dfrac{11}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}=\dfrac{9}{15}-\dfrac{11}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}=-\dfrac{2}{15}\\\\\dfrac{3}{5}-\dfrac{11}{15}<0\\\\\dfrac{3}{5}<\dfrac{11}{15} [/tex]

a >       7/9  = 21 /27  donc 7/9 > 20/27

b  >       3/5 = 9/15   donc   3/5  < 11/15