a)1/2x+3/5x=-33/22 b) (2/3x -4/7).(1/2+-3/7:x)=0 c) (4/5-2x).(1/3+3/5:x)=0

Đáp án:

$\begin{array}{l}
a)\dfrac{1}{2}x + \dfrac{3}{5}x =  - \dfrac{{33}}{{22}}\\
 \Leftrightarrow \left( {\dfrac{1}{2} + \dfrac{3}{5}} \right).x = \dfrac{{ - 3}}{2}\\
 \Leftrightarrow \dfrac{{11}}{{10}}.x =  - \dfrac{3}{2}\\
 \Leftrightarrow x =  - \dfrac{3}{2}.\dfrac{{10}}{{11}}\\
 \Leftrightarrow x =  - \dfrac{{15}}{{11}}\\
Vậy\,x =  - \dfrac{{15}}{{11}}\\
b)\left( {\dfrac{2}{3}x - \dfrac{4}{7}} \right).\left( {\dfrac{1}{2} + \dfrac{{ - 3}}{7}:x} \right) = 0\\
 \Leftrightarrow \left[ \begin{array}{l}
\dfrac{2}{3}.x - \dfrac{4}{7} = 0\\
\dfrac{1}{2} + \dfrac{{ - 3}}{7}:x = 0
\end{array} \right.\\
 \Leftrightarrow \left[ \begin{array}{l}
\dfrac{2}{3}.x = \dfrac{4}{7}\\
\dfrac{3}{7}:x = \dfrac{1}{2}
\end{array} \right.\\
 \Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{4}{7}.\dfrac{3}{2} = \dfrac{6}{7}\\
x = \dfrac{3}{7}:\dfrac{1}{2} = \dfrac{6}{7}
\end{array} \right.\\
Vậy\,x = \dfrac{6}{7}\\
c)\left( {\dfrac{4}{5} - 2x} \right).\left( {\dfrac{1}{3} + \dfrac{3}{5}:x} \right) = 0\\
 \Leftrightarrow \left[ \begin{array}{l}
\dfrac{4}{5} - 2x = 0\\
\dfrac{1}{3} + \dfrac{3}{5}:x = 0
\end{array} \right.\\
 \Leftrightarrow \left[ \begin{array}{l}
2x = \dfrac{4}{5}\\
\dfrac{3}{5}:x =  - \dfrac{1}{3}
\end{array} \right.\\
 \Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{2}{5}\\
x = \dfrac{3}{5}.\left( { - 3} \right) =  - \dfrac{9}{5}
\end{array} \right.\\
Vậy\,x = \dfrac{2}{5};x =  - \dfrac{9}{5}
\end{array}$