Đáp án:
\(\begin{array}{l}
B1:\\
a)\dfrac{1}{{15}}\\
b)1\\
c)\dfrac{5}{3}\\
d)0\\
B2:\\
a)x = 2\\
b)x = - 3\\
c)\left[ \begin{array}{l}
x = 2\\
x = - \dfrac{{43}}{{10}}
\end{array} \right.\\
d)x = 3
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
B1:\\
a) - \dfrac{1}{3} + \dfrac{2}{5}\\
= \dfrac{{ - 5 + 6}}{{15}} = \dfrac{1}{{15}}\\
b){\left( {\dfrac{1}{8}} \right)^3}{.8^3} = 1\\
c)\dfrac{7}{3} + \dfrac{4}{7}:\dfrac{{ - 6}}{7}\\
= \dfrac{7}{3} - \dfrac{4}{7}.\dfrac{7}{6}\\
= \dfrac{7}{3} - \dfrac{2}{3}\\
= \dfrac{5}{3}\\
d)\dfrac{{ - 3.5 + 2.4}}{{20}}:\dfrac{3}{7} + \dfrac{{12 - 5}}{{20}}:\dfrac{3}{7}\\
= \left( {\dfrac{{ - 7}}{{20}} + \dfrac{7}{{20}}} \right):\dfrac{3}{7} = 0:\dfrac{3}{7} = 0\\
B2:\\
a)x - \dfrac{1}{3} = \dfrac{5}{3}\\
\to x = \dfrac{5}{3} + \dfrac{1}{3}\\
\to x = 2\\
b)\dfrac{{x - 3}}{{15}} = - \dfrac{2}{5}\\
\to x - 3 = - 6\\
\to x = - 3\\
c)\left| {2x + \dfrac{{23}}{{10}}} \right| = \dfrac{{14}}{5} + \dfrac{7}{2}\\
\to \left| {2x + \dfrac{{23}}{{10}}} \right| = \dfrac{{28 + 35}}{{10}}\\
\to \left| {2x + \dfrac{{23}}{{10}}} \right| = \dfrac{{63}}{{10}}\\
\to \left[ \begin{array}{l}
2x + \dfrac{{23}}{{10}} = \dfrac{{63}}{{10}}\\
2x + \dfrac{{23}}{{10}} = - \dfrac{{63}}{{10}}
\end{array} \right.\\
\to \left[ \begin{array}{l}
2x = 4\\
2x = - \dfrac{{43}}{5}
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 2\\
x = - \dfrac{{43}}{{10}}
\end{array} \right.\\
d){2^x} + {2^x}{.2^3} = 8.9\\
\to {2^x} + {8.2^x} = 72\\
\to {9.2^x} = 72\\
\to {2^x} = 8\\
\to {2^x} = {2^3}\\
\to x = 3
\end{array}\)
