tìm x a ) 2/7 + x = -5/4 b ) x – 11/7 = 13/3 c ) 12/5 – x = -9/4 d ) -x – 4/5 = -6/5 e ) 2/3 – ( -1/2 – x ) = -4/5 f ) 3/7 – x = 1/4 – ( -3 / 5

0 bình luận về “tìm x a ) 2/7 + x = -5/4 b ) x – 11/7 = 13/3 c ) 12/5 – x = -9/4 d ) -x – 4/5 = -6/5 e ) 2/3 – ( -1/2 – x ) = -4/5 f ) 3/7 – x = 1/4 – ( -3 / 5”

1. Đáp án:

   $\begin{array}{l}
   a)\dfrac{2}{7} + x = \dfrac{{ – 5}}{4}\\
   x = \dfrac{{ – 5}}{4} – \dfrac{2}{7}\\
   x = \dfrac{{ – 35 – 8}}{{28}}\\
   x =  – \dfrac{{43}}{{28}}\\
   Vậy\,x = \dfrac{{ – 43}}{{28}}\\
   b)x – \dfrac{{11}}{7} = \dfrac{{13}}{3}\\
   x = \dfrac{{13}}{3} + \dfrac{{11}}{7}\\
   x = \dfrac{{91 + 33}}{{21}}\\
   x = \dfrac{{124}}{{21}}\\
   Vậy\,x = \dfrac{{124}}{{21}}\\
   c)\dfrac{{12}}{5} – x = \dfrac{{ – 9}}{4}\\
   x = \dfrac{{12}}{5} – \left( { – \dfrac{9}{4}} \right)\\
   x = \dfrac{{12}}{5} + \dfrac{9}{4}\\
   x = \dfrac{{93}}{{20}}\\
   Vậy\,x = \dfrac{{93}}{{20}}\\
   d) – x – \dfrac{4}{5} = \dfrac{{ – 6}}{5}\\
   x = \dfrac{{ – 4}}{5} + \dfrac{6}{5}\\
   x = \dfrac{2}{5}\\
   e)\dfrac{2}{3} – \left( { – \dfrac{1}{2} – x} \right) = \dfrac{{ – 4}}{5}\\
   \dfrac{2}{3} + \dfrac{1}{2} + x = \dfrac{{ – 4}}{5}\\
   x =  – \dfrac{4}{5} – \dfrac{2}{3} – \dfrac{1}{2}\\
   x = \dfrac{{ – 24 – 20 – 15}}{{30}}\\
   x = \dfrac{{ – 59}}{{30}}\\
   Vậy\,x = \dfrac{{ – 59}}{{30}}\\
   g)\dfrac{{ – 21}}{{10}}.x + \dfrac{1}{3} = \dfrac{{ – 2}}{3}\\
   \dfrac{{ – 21}}{{10}}.x = \dfrac{{ – 2}}{3} – \dfrac{1}{3} =  – 1\\
   x = \dfrac{{10}}{{21}}\\
   Vậy\,x = \dfrac{{10}}{{21}}\\
   h)\dfrac{8}{{15}}:x = \dfrac{{ – 20}}{{21}}\\
   x = \dfrac{8}{{15}}:\dfrac{{ – 20}}{{21}}\\
   x = \dfrac{8}{{15}}.\dfrac{{ – 21}}{{20}}\\
   x = \dfrac{{ – 14}}{{25}}\\
   Vậy\,x = \dfrac{{ – 14}}{{25}}\\
   i)x:\left( { – \dfrac{4}{{21}}} \right) = \dfrac{{14}}{5}\\
   x = \dfrac{{14}}{5}.\dfrac{{ – 4}}{{21}}\\
   x = \dfrac{{ – 8}}{{15}}\\
   Vậy\,x = \dfrac{{ – 8}}{{15}}
   \end{array}$

   Trả lời