Bài 1:Tìm x biết: a, (3,25- 2/3x).(-7/4)=-3 b,7/4-3/4:x=7/16 c,5/2-3/4x=4/5 d,3/5x+(-1)/2=-7/10 e,4/15:x+(-1)/3=5/9

Đáp án:

e) \(x = \dfrac{3}{{10}}\) 

Giải thích các bước giải:

\(\begin{array}{l}
a)\left( {\dfrac{{13}}{4} - \dfrac{2}{3}x} \right).\left( { - \dfrac{7}{4}} \right) =  - 3\\
 \to \dfrac{{13}}{4} - \dfrac{2}{3}x = \dfrac{{12}}{7}\\
 \to \dfrac{2}{3}x = \dfrac{{43}}{{28}}\\
 \to x = \dfrac{{129}}{{56}}\\
b)DK:x \ne 0\\
\dfrac{7}{4} - \dfrac{3}{4}:x = \dfrac{7}{{16}}\\
 \to \dfrac{3}{4}:x = \dfrac{{21}}{{16}}\\
 \to x = \dfrac{3}{4}:\dfrac{{21}}{{16}}\\
 \to x = \dfrac{4}{7}\\
c)DK:x \ne 0\\
\dfrac{5}{2} - \dfrac{3}{{4x}} = \dfrac{4}{5}\\
 \to \dfrac{3}{{4x}} = \dfrac{5}{2} - \dfrac{4}{5}\\
 \to \dfrac{3}{{4x}} = \dfrac{{17}}{{10}}\\
 \to x = \dfrac{{15}}{{34}}\\
d)\dfrac{3}{5}x - \dfrac{1}{2} =  - \dfrac{7}{{10}}\\
 \to \dfrac{3}{5}x =  - \dfrac{1}{5}\\
 \to x =  - \dfrac{1}{3}\\
e)\dfrac{4}{{15}}:x - \dfrac{1}{3} = \dfrac{5}{9}\\
 \to \dfrac{4}{{15}}:x = \dfrac{8}{9}\\
 \to x = \dfrac{3}{{10}}
\end{array}\)