Tìm x a)7/8+ 4 1/2:x=-13/40 b)(x-2 1/4):(-5/6=3 c)4 2/3-(3/5:x=-20% d)70%x=1 1/2+2.2x Em cần gấp ạ

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1. Đáp án:

    $a)x=\dfrac{-15}{4}\\
   b) x=\dfrac{-1}{4}\\
   c) x=\dfrac{9}{73}\\
   d) x=-\dfrac{5}{11}$

   Giải thích các bước giải:

    $a) \dfrac{7}{8}+4\dfrac{1}{2}:x=-\dfrac{13}{40}\\
   \Leftrightarrow \dfrac{9}{2}.\dfrac{1}{x}=-\dfrac{13}{40}-\dfrac{7}{8}\\
   \Leftrightarrow \dfrac{9}{2}.\dfrac{1}{x}=-\dfrac{13}{40}-\dfrac{35}{40}\\
   \Leftrightarrow \dfrac{9}{2}.\dfrac{1}{x}=-\dfrac{48}{40}=\dfrac{-6}{5}\\
   \Leftrightarrow x=\dfrac{9}{2}.\dfrac{-5}{6}=\dfrac{-15}{4}\\
   b) (x-2\dfrac{1}{4}):(-\dfrac{5}{6})=3\\
   \Leftrightarrow (x-\dfrac{9}{4}).(-\dfrac{6}{5})=3\\
   \Leftrightarrow x-\dfrac{9}{4}=3.\dfrac{-5}{6}\\
   \Leftrightarrow x=\dfrac{-5}{2}+\dfrac{9}{4}\\
   \Leftrightarrow x=\dfrac{-10}{4}+\dfrac{9}{4}\\
   \Leftrightarrow x=\dfrac{-1}{4}\\
   c) 4\dfrac{2}{3}-(\dfrac{3}{5}):x=-20.\dfrac{1}{100}\\
   \Leftrightarrow \dfrac{14}{3}-\dfrac{3}{5}.\dfrac{1}{x}=-\dfrac{1}{5}\\
   \Leftrightarrow -\dfrac{3}{5}\dfrac{1}{x}=\dfrac{-1}{5}-\dfrac{14}{3}\\
   \Leftrightarrow -\dfrac{3}{5}\dfrac{1}{x}=\dfrac{-3}{15}-\dfrac{14.5}{15}\\
   \Leftrightarrow -\dfrac{3}{5}\dfrac{1}{x}=\dfrac{-73}{15}\\
   \Leftrightarrow x=\dfrac{-3}{5}.\dfrac{-15}{73}=\dfrac{9}{73}\\
   d) \dfrac{70}{100}x=1\dfrac{1}{2}+2.2x\\
   \Leftrightarrow \dfrac{7}{10}x=\dfrac{3}{2}+4x\\
   \Leftrightarrow \left (\dfrac{7}{10}-4  \right )x=\dfrac{3}{2}\\
   \Leftrightarrow \left (\dfrac{7}{10}-\dfrac{4.10}{10}  \right )x=\dfrac{3}{2}\\
   \Leftrightarrow \dfrac{-33}{10}x=\dfrac{3}{2}\\
   \Leftrightarrow x=\dfrac{3}{2}.\dfrac{-10}{33}=-\dfrac{5}{11}$

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