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) \(\left( {\dfrac{3}{2} - x} \right):\dfrac{{ - 14}}{3} = \dfrac{{ - 6}}{7}\).
Phương pháp giải - Xem chi tiết
Ta tìm giá trị của x dựa vào các biểu thức đã cho.
Lời giải chi tiết
a)
\(\begin{array}{l}x + \left( { - \dfrac{2}{5}} \right) = \dfrac{{ - 1}}{3}\\{\rm{ }}x = \dfrac{{ - 1}}{3} - \left( { - \dfrac{2}{5}} \right)\\{\rm{ }}x = \dfrac{{ - 1}}{3} + \dfrac{2}{5}\\{\rm{ }}x = \dfrac{{ - 5}}{15} + \dfrac{6}{15}\\{\rm{ }}x = \dfrac{1}{{15}}\end{array}\)
Vậy \(x = \dfrac{1}{{15}}\).
b)
\(\begin{array}{l}0,5 - x = \dfrac{{ - 5}}{{14}}\\{\rm{ }}x = 0,5 - \dfrac{{ - 5}}{{14}}\\{\rm{ }}x = \dfrac{1}{2} + \dfrac{5}{{14}}\\{\rm{ }}x = \dfrac{7}{14} + \dfrac{5}{{14}}\\{\rm{ }}x = \dfrac{12}{14}\\{\rm{ }}x = \dfrac{6}{7}\end{array}\)
Vậy \(x = \dfrac{6}{7}\).
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 \(x = \dfrac{{ - 5}}{2}\).
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