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Đáp án:

Giải thích các bước giải:

$3.\\a)\dfrac{-2}{13} + \dfrac{-11}{26}\\=\dfrac{-4}{26} +\dfrac{-11}{26} \\ = \dfrac{-15}{26}\\b)-3\dfrac{1}{2} - 2\dfrac{1}{4}\\ = \dfrac{-7}{2} - \dfrac{9}{4}\\=\dfrac{-12}{4} \\= -3\\c)(-4) - \bigg(-\dfrac{4}{5}\bigg)\\ = \dfrac{-20}{5} - \dfrac{-4}{5} \\ = \dfrac{-16}{5}\\d)\dfrac{-6}{7} . \dfrac{21}{12} \\ = \dfrac{-6 . 21}{7 . 12}\\ = \dfrac{-3}{2}\\e)\dfrac{-31}{36} : \dfrac{37}{-72}\\= \dfrac{-31}{36} . \dfrac{-72}{37}\\ = \dfrac{62}{37}\\f)\bigg(\dfrac{-5}{17}\bigg) : (- 15)\\ = \dfrac{-5}{17} . \dfrac{1}{-15} \\ = \dfrac{1}{51}$

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