Giải thích các bước giải:
\(\begin{array}{l}
1,\\
a,\\
\dfrac{{11}}{{12}} - \left( {\dfrac{2}{5} + x} \right) = \dfrac{2}{3}\\
\Leftrightarrow \dfrac{2}{5} + x = \dfrac{{11}}{{12}} - \dfrac{2}{3}\\
\Leftrightarrow \dfrac{2}{5} + x = \dfrac{1}{4}\\
\Leftrightarrow x = \dfrac{1}{4} - \dfrac{2}{5}\\
\Leftrightarrow x = - \dfrac{3}{{20}}\\
b,\\
2x.\left( {x - \dfrac{1}{7}} \right) = 0\\
\Leftrightarrow x.\left( {x - \dfrac{1}{7}} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = 0\\
x - \dfrac{1}{7} = 0
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x = 0\\
x = \dfrac{1}{7}
\end{array} \right.\\
c,\\
- \dfrac{3}{4} < \dfrac{x}{{12}} < - \dfrac{5}{9}\\
\Leftrightarrow - \dfrac{3}{4}.12 < x < - \dfrac{5}{9}.12\\
\Leftrightarrow - 9 < x < - \dfrac{{20}}{3}\\
d,\\
- \dfrac{5}{6} < \dfrac{x}{5} < \dfrac{1}{2}\\
\Leftrightarrow - \dfrac{5}{6}.5 < x < \dfrac{1}{2}.5\\
\Leftrightarrow - \dfrac{{25}}{6} < x < \dfrac{5}{2}\\
2,\\
a,\\
0,25.\dfrac{{ - 15}}{4} = \dfrac{1}{4}.\dfrac{{ - 15}}{4} = - \dfrac{{15}}{{16}}\\
b,\\
- 2.\dfrac{{ - 7}}{{12}} = 2.\dfrac{7}{{12}} = \dfrac{7}{6}\\
c,\\
\dfrac{{ - 3}}{{25}}:6 = \dfrac{{ - 3}}{{25}}.\dfrac{1}{6} = \dfrac{{ - 1}}{{50}}\\
d,\\
\dfrac{2}{3} + \dfrac{3}{4}.\left( { - \dfrac{4}{9}} \right) = \dfrac{2}{3} + \dfrac{{ - 1}}{3} = \dfrac{1}{3}\\
e,\\
2.\dfrac{3}{{11}}.1\dfrac{1}{{12}}.\left( { - 2,2} \right) = 2.\dfrac{3}{{11}}.\dfrac{{13}}{{12}}.\dfrac{{ - 11}}{5}\\
= \dfrac{{ - 2.3.13}}{{12.5}} = \dfrac{{ - 2.3.13}}{{2.2.3.5}} = \dfrac{{ - 13}}{{2.5}} = - \dfrac{{13}}{{10}}\\
g,\\
\left( {\dfrac{3}{4} - 0,2} \right).\left( {0,4 - \dfrac{4}{5}} \right)\\
= \left( {\dfrac{3}{4} - \dfrac{1}{5}} \right).\left( {\dfrac{2}{5} - \dfrac{4}{5}} \right)\\
= \dfrac{{11}}{{20}}.\dfrac{{ - 2}}{5}\\
= \dfrac{{ - 11}}{{50}}\\
3,\\
a,\\
x + \dfrac{2}{3} = \dfrac{5}{6}\\
\Leftrightarrow x = \dfrac{5}{6} - \dfrac{2}{3}\\
\Leftrightarrow x = \dfrac{1}{6}\\
b,\\
\dfrac{3}{7} - \left( {\dfrac{1}{2} - x} \right) = \dfrac{{ - 1}}{3}\\
\Leftrightarrow \dfrac{1}{2} - x = \dfrac{3}{7} - \dfrac{{ - 1}}{3}\\
\Leftrightarrow \dfrac{1}{2} - x = \dfrac{{16}}{{21}}\\
\Leftrightarrow x = \dfrac{1}{2} - \dfrac{{16}}{{21}}\\
\Leftrightarrow x = - \dfrac{{11}}{{42}}\\
c,\\
\left( {x - \dfrac{3}{4}} \right) + \dfrac{1}{2} = \dfrac{5}{8}\\
\Leftrightarrow x - \dfrac{3}{4} = \dfrac{5}{8} - \dfrac{1}{2}\\
\Leftrightarrow x - \dfrac{3}{4} = \dfrac{1}{8}\\
\Leftrightarrow x = \dfrac{1}{8} + \dfrac{3}{4}\\
\Leftrightarrow x = \dfrac{7}{8}
\end{array}\)
