Đáp án:
b. \(x = \frac{1}{2}\)
Giải thích các bước giải:
\(\begin{array}{l}
a.\left| {2x + 1} \right| = 3 + \left| {5x - 2} \right|\\
\to 4{x^2} + 4x + 1 = 9 + 6\left( {5x - 2} \right) + 25{x^2} - 20x + 4\\
\to 21{x^2} + 6x = 0\\
\to 3x\left( {7x + 2} \right) = 0\\
\to \left[ \begin{array}{l}
x = 0\\
x = - \frac{2}{7}
\end{array} \right.\\
b.\left| {x + 1} \right| - 2\left| {x + 1} \right| = x\\
\to - \left| {x + 1} \right| = x\\
\to \left[ \begin{array}{l}
- x - 1 = x\\
x + 1 = x
\end{array} \right.\\
\to \left[ \begin{array}{l}
2x = 1\\
1 = 0\left( {vô lý} \right)
\end{array} \right.\\
\to x = \frac{1}{2}
\end{array}\)
