1/3 . 4/5 + 1/3 . 1 1/5 - ( -2/3 ) mũ 1 1 là hỗn số x/7 = -6/21 | x - 1/5 | - 1/2 = 0

Đáp án: $x = \dfrac{7}{{10}};x =  - \dfrac{3}{{10}}$

Giải thích các bước giải:

$\begin{array}{l}
\dfrac{1}{3}.\dfrac{4}{5} + \dfrac{1}{3}.1\dfrac{1}{5} - {\left( { - \dfrac{2}{3}} \right)^1}\\
 = \dfrac{1}{3}.\dfrac{4}{5} + \dfrac{1}{3}.\dfrac{6}{5} - \left( { - \dfrac{2}{3}} \right)\\
 = \dfrac{1}{3}.\dfrac{4}{5} + \dfrac{1}{3}.\dfrac{6}{5} + 2.\dfrac{1}{3}\\
 = \dfrac{1}{3}.\left( {\dfrac{4}{5} + \dfrac{6}{5} + 2} \right)\\
 = \dfrac{1}{3}.\left( {\dfrac{{10}}{5} + 2} \right)\\
 = \dfrac{1}{3}.\left( {2 + 2} \right)\\
 = \dfrac{4}{3}\\
b)\dfrac{x}{7} =  - \dfrac{6}{{21}}\\
 \Leftrightarrow \dfrac{x}{7} = \dfrac{{ - 2}}{7}\\
 \Leftrightarrow x =  - \dfrac{2}{7}.7\\
 \Leftrightarrow x =  - 2\\
Vay\,x =  - 2\\
c)\left| {x - \dfrac{1}{5}} \right| - \dfrac{1}{2} = 0\\
 \Leftrightarrow \left| {x - \dfrac{1}{5}} \right| = \dfrac{1}{2}\\
 \Leftrightarrow \left[ \begin{array}{l}
x - \dfrac{1}{5} = \dfrac{1}{2}\\
x - \dfrac{1}{5} =  - \dfrac{1}{2}
\end{array} \right.\\
 \Leftrightarrow \left[ \begin{array}{l}
x = \dfrac{1}{2} + \dfrac{1}{5} = \dfrac{7}{{10}}\\
x =  - \dfrac{1}{2} + \dfrac{1}{5} = \dfrac{{ - 3}}{{10}}
\end{array} \right.\\
Vậy\,x = \dfrac{7}{{10}};x =  - \dfrac{3}{{10}}
\end{array}$