a,\(\dfrac{4}{5}và\dfrac{3}{7}=\dfrac{4.7}{5.7}và\dfrac{3.5}{7.5}=\dfrac{28}{35}và\dfrac{15}{35}=>\dfrac{4}{5}>\dfrac{3}{7}\)
b,\(\dfrac{11}{15}và\dfrac{12}{16}=\dfrac{11}{15}và\dfrac{3}{4}=\dfrac{11.4}{15.4}và\dfrac{3.15}{4.15}=\dfrac{44}{60}và\dfrac{45}{60}=>\dfrac{11}{15}< \dfrac{12}{16}\)
Mk làm 2 câu này trước
c,\(\dfrac{-3}{7}và\dfrac{-4}{9}=\dfrac{-3.9}{7.9}và\dfrac{-4.7}{9.7}=\dfrac{-27}{63}và\dfrac{-28}{63}=>\dfrac{-3}{7}>\dfrac{-4}{9}\)
d,\(\dfrac{-5}{8}và\dfrac{4}{-7}=\dfrac{-5}{8}và\dfrac{-4}{7}=\dfrac{-5.7}{8.7}và\dfrac{-4.8}{7.8}=\dfrac{-35}{56}và\dfrac{-32}{56}=>\dfrac{-5}{8}< \dfrac{4}{-7}\)
e,\(\dfrac{-7}{8}và\dfrac{30}{-42}=\dfrac{-7}{8}và\dfrac{-5}{7}=\dfrac{-7.7}{8.7}và\dfrac{-5.8}{7.8}=\dfrac{-49}{56}và\dfrac{-40}{56}=>\dfrac{-7}{8}< \dfrac{30}{-42}\)
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