Đáp án:
B2:
d) x=5
Giải thích các bước giải:
\(\begin{array}{l}
B1:\\
a) - \dfrac{3}{{21}} - \dfrac{2}{7} = - \dfrac{1}{7} - \dfrac{2}{7} = - \dfrac{3}{7}\\
c)1 - \left( {8.2} \right) = 1 - 16 = - 15\\
b) - \dfrac{{43}}{{10}}.7 - \dfrac{{57}}{{10}}.7\\
= 7\left( { - \dfrac{{43}}{{10}} - \dfrac{{57}}{{10}}} \right)\\
= 7.\left( { - 10} \right) = - 70\\
d)7 + 4 = 11\\
B2:\\
a)x = - 3,2 + 1,2\\
\to x = - 2\\
c)\left| x \right| - \dfrac{1}{2} = \dfrac{1}{2}\\
\to \left| x \right| = \dfrac{1}{4}\\
\to \left[ \begin{array}{l}
x = \dfrac{1}{4}\\
x = - \dfrac{1}{4}
\end{array} \right.\\
b) - x = - \dfrac{1}{8} + \dfrac{3}{4}\\
\to - x = \dfrac{5}{8}\\
\to x = - \dfrac{5}{8}\\
d)\dfrac{{1 - x}}{{20}} = - \dfrac{1}{5}\\
\to 5 - 5x = - 20\\
\to 5x = 25\\
\to x = 5
\end{array}\)
