Bài 1: a) 1/7 . x = -3/2 b) 2/15 – x = -7/45 c) 2 . ( 3/24 – x ) = 3/4 = 5/12

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1. Đáp án:

    a/$x=\frac{-21}{2}$

   b/$x=\frac{13}{45}$

   c/$x = \frac{7}{24}$

   Giải thích các bước giải:

   a/$\frac{1}{7}.x=\frac{-3}{2}$

   $x=\frac{-3}{2} : \frac{1}{7}$

   $x=\frac{-21}{2}$

   .

   b/$\frac{2}{15}-x=\frac{-7}{45}$

   $x=\frac{2}{15}-\frac{-7}{45}$

   $x=\frac{13}{45}$

   .

   c/$2 . (\frac{3}{24} – x )+ \frac{3}{4}= \frac{5}{12}$

   $2 . (\frac{3}{24} – x )= \frac{5}{12}- \frac{3}{4}$

   $2 . (\frac{3}{24} – x ) = \frac{-1}{3}$

   $\frac{3}{24} – x = \frac{-1}{3} :2$

   $\frac{3}{24} – x = \frac{-1}{6}$

   $x = \frac{3}{24} – \frac{-1}{6}$

   $x = \frac{7}{24}$

   $#minhthong2009$

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2. Đáp án:

   a) `x=-21/2`

   b) `x=13/45`

   c)  `x = 7/24`

   Giải thích các bước giải:

   a) `1/7 . x = -3/2`

   `to x = -3/2 : 1/7`

   `to x = -3/2 . 7`

   `to x = -21/2`

   Vậy `x = -21/2`

   b) `2/15 – x = -7/45`

   `to x = 2/15 – ( -7/45 )`

   `to x = 2/15 + 7/45`

   `to x = 6/45 + 7/45`

   `to x = 13/45`

   Vậy `x = 13/45`

   c) `2 . ( 3/24 – x ) + 3/4 = 5/12`

   `to 2 . ( 3/24 – x ) = 5/12 – 3/4`

   `to 2 . ( 3/24 – x ) = 5/12 – 9/12`

   `to 2 . ( 3/24 – x ) = -1/3`

   `to 3/24 – x = -1/3 : 2`

   `to 3/24 – x = -1/3 . 1/2`

   `to 3/24 – x = -1/6`

   `to x = 3/24 – ( -1/6 )`

   `to x = 3/24 + 1/6`

   `to x = 3/24 + 4/24`

   `to x = 7/24`

   Vậy `x = 7/24`

    

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