Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
3,\\
\left| a \right| = 1,6 \Rightarrow \left[ \begin{array}{l}
a = 1,6\\
a = - 1,6
\end{array} \right.\\
TH1:\,\,\,\,a = 1,6\,;\,\,\,\,\,b = - 0,75\\
M = a + 2ab - b = 1,6 + 2.1,6.\left( { - 0,75} \right) - \left( { - 0,75} \right)\\
= 1,6 - 2.1,6.0,75 + 0,75\\
= - 0,05\\
TH2:\,\,\,\,\,a = - 1,6\,;\,\,\,\,\,b = - 0,75\\
M = a + 2ab - b = - 1,6 + 2.\left( { - 1,6} \right).\left( { - 0,75} \right) - \left( { - 0,75} \right)\\
= - 1,6 + 2.1,6.0,75 + 0,75\\
= 1,55\\
4,\\
a,\\
\left| {\dfrac{1}{2}x} \right| = 3 - 2x\\
\Leftrightarrow \left\{ \begin{array}{l}
3 - 2x \ge 0\\
\left[ \begin{array}{l}
\dfrac{1}{2}x = 3 - 2x\\
\dfrac{1}{2}x = 2x - 3
\end{array} \right.
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \le \dfrac{3}{2}\\
\left[ \begin{array}{l}
\dfrac{5}{2}x = 3\\
\dfrac{3}{2}x = 3
\end{array} \right.
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \le \dfrac{3}{2}\\
\left[ \begin{array}{l}
x = \dfrac{6}{5}\\
x = 2
\end{array} \right.
\end{array} \right. \Leftrightarrow x = \dfrac{6}{5}\\
b,\\
\left| {x - 1} \right| = 3x + 2\\
\Leftrightarrow \left\{ \begin{array}{l}
3x + 2 \ge 0\\
\left[ \begin{array}{l}
x - 1 = 3x + 2\\
x - 1 = - 3x - 2
\end{array} \right.
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \ge - \dfrac{2}{3}\\
\left[ \begin{array}{l}
2x = - 3\\
- 4x = 1
\end{array} \right.
\end{array} \right. \Leftrightarrow \left\{ \begin{array}{l}
x \ge - \dfrac{2}{3}\\
\left[ \begin{array}{l}
x = - \dfrac{3}{2}\\
x = - \dfrac{1}{4}
\end{array} \right.
\end{array} \right. \Leftrightarrow x = - \dfrac{1}{4}
\end{array}\)
