Đề bài

Tìm x: a) \(x + \left( { - \dfrac{2}{5}} \right) = \dfrac{{ - 1}}{3}\);                                            b) \(0,5 - x = \dfrac{{ - 5}}{{14}}\); c) \(( - 0,4).\left( {2x + \dfrac{2}{5}} \right) =  - 9,4\);                 d) \(\left( {\dfrac{3}{2} - x} \right):\dfrac{{ - 14}}{3} = \dfrac{{ - 6}}{7}\).

Lời giải chi tiết

c) \(\begin{array}{l}( - 0,4).\left( {2x + \dfrac{2}{5}} \right) =  - 9,4\\{\rm{  }}2x + \dfrac{2}{5} =  (- 9,4) : ( - 0,4)\\{\rm{  }}2x + \dfrac{2}{5} =  \dfrac{47}{2}\\{\rm{  }}2x =  \dfrac{47}{2} - \dfrac{2}{5}\\{\rm{  }}2x = \dfrac{{ 231}}{10}\\{\rm{  }}x = \dfrac{{ 231}}{10}:2\\{\rm{  }}x = \dfrac{{ 231}}{{20}}\end{array}\)Vậy \(x = \dfrac{{ 231}}{{20}}\).                                    d) \(\begin{array}{l}\left( {\dfrac{3}{2} - x} \right):\dfrac{{ - 14}}{3} = \dfrac{{ - 6}}{7}\\{\rm{  }}\dfrac{3}{2} - x = \dfrac{{ - 6}}{7}.\dfrac{{ - 14}}{3}\\{\rm{  }}\dfrac{3}{2} - x = 4\\{\rm{  }}x = \dfrac{3}{2} - 4\\{\rm{  }}x = \dfrac{3}{2} - \dfrac{8}{2}\\{\rm{  }}x = \dfrac{{ - 5}}{2}\end{array}\)Vậy \(x = \dfrac{{ - 5}}{2}\).