Tìm x : a) 2/5x + 7/3 = 15/2 b)1/3/x – 7/4= 5/6 c) 1/4 – 2/3x = 3/4 d) 2/3x – 3/4x =1/3 Các bn ơi giúp mik bài này là tìm x phân số nha các bn

Đáp án:

$\begin{array}{l}
a)\dfrac{2}{5}x + \dfrac{7}{3} = \dfrac{{15}}{2}\\
 \Rightarrow \dfrac{2}{5}x = \dfrac{{15}}{2} – \dfrac{7}{3}\\
 \Rightarrow \dfrac{2}{5}x = \dfrac{{45 – 14}}{6}\\
 \Rightarrow \dfrac{2}{5}x = \dfrac{{31}}{6}\\
 \Rightarrow x = \dfrac{{31}}{6}.\dfrac{5}{2}\\
 \Rightarrow x = \dfrac{{155}}{{12}}\\
\text{Vậy}\,x = \dfrac{{155}}{{12}}\\
b)\dfrac{1}{3}x – \dfrac{7}{4} = \dfrac{5}{6}\\
 \Rightarrow \dfrac{1}{3}x = \dfrac{5}{6} + \dfrac{7}{4}\\
 \Rightarrow \dfrac{1}{3}x = \dfrac{{10 + 21}}{{12}}\\
 \Rightarrow \dfrac{1}{3}x = \dfrac{{31}}{{12}}\\
 \Rightarrow x = \dfrac{{31}}{{12}}.3 = \dfrac{{31}}{4}\\
\text{Vậy}\,x = \dfrac{{31}}{4}\\
c)\dfrac{1}{4} – \dfrac{2}{3}x = \dfrac{3}{4}\\
 \Rightarrow \dfrac{2}{3}x = \dfrac{1}{4} – \dfrac{3}{4} =  – \dfrac{1}{2}\\
 \Rightarrow x = \dfrac{{ – 1}}{2}:\dfrac{2}{3}\\
 \Rightarrow x = \dfrac{{ – 1}}{2}.\dfrac{3}{2}\\
 \Rightarrow x =  – \dfrac{3}{4}\\
\text{Vậy}\,x =  – \dfrac{3}{4}\\
d)\dfrac{2}{3}x – \dfrac{3}{4}x = \dfrac{1}{3}\\
 \Rightarrow \left( {\dfrac{2}{3} – \dfrac{3}{4}} \right).x = \dfrac{1}{3}\\
 \Rightarrow \dfrac{{ – 1}}{{12}}.x = \dfrac{1}{3}\\
 \Rightarrow x = \dfrac{1}{3}.\left( { – 12} \right)\\
 \Rightarrow x =  – 4\\
\text{Vậy}\,x =  – 4
\end{array}$