Bài 1: Tính hợp lí a) 3/8+ 6/(-18) – (-9)/27 – 2/(-16) b ) ( 13/5 – 7/(-16) – ( 15/6 -6/15 ) c) 3/17 – 5/13 – 14 / (-17) + 18/ (-35) – ( -8 ) / (-13

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1. Đáp án + Giải thích các bước giải:

   a)
   $\dfrac{3}{8}+\dfrac{6}{-18}-\dfrac{-9}{27}-\dfrac{2}{-16}$

   $=\dfrac{3}{8}+\dfrac{-1}{3}-\dfrac{-1}{3}-\dfrac{-1}{13}$

   $=(\dfrac{-1}{3}-\dfrac{-1}{3}) – \dfrac{3}{8}+\dfrac{-1}{13}$

   $=0 – \dfrac{3}{8}+\dfrac{-1}{13}$

   $=\dfrac{-3}{8}+\dfrac{-1}{13}$

   $=\dfrac{-39}{104}+\dfrac{-8}{104}$

   $=\dfrac{-47}{104}$

   b)

   $(\dfrac{13}{5}-\dfrac{7}{16}) – (\dfrac{15}{6} -\dfrac{6}{15})$ 

   $=\dfrac{13}{5}-\dfrac{7}{16} – \dfrac{5}{2} +\dfrac{2}{5}$

   $=(\dfrac{13}{5}+\dfrac{2}{5})-\dfrac{7}{16} – \dfrac{5}{2}$

   $=3 – \dfrac{7}{16} – \dfrac{5}{2}$

   $=\dfrac{41}{16} – \dfrac{5}{2}$

   $=\dfrac{41}{16} – \dfrac{40}{16}$

   $=\dfrac{1}{16}$

   c)

   $\dfrac{3}{17} – \dfrac{5}{13} – \dfrac{14}{-17} + \dfrac{18}{-35} – \dfrac{-8}{13} – \dfrac{7}{35}$

   $=(\dfrac{3}{17}- \dfrac{14}{-17}) -(\dfrac{5}{13}- \dfrac{-8}{13}) + (\dfrac{18}{-35}- \dfrac{7}{35})$

   $=1-1+\dfrac{-11}{35}$

   $=0+\dfrac{-11}{35}$

   $=\dfrac{-11}{35}$

    

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