2 câu trả lời
Đáp án:
Giải thích các bước giải: $\begin{array}{l} \left| {x\left( {x + 5} \right)} \right| = 4x \Leftrightarrow \left\{ \begin{array}{l} 4x \ge 0\\ {x^2}{\left( {x + 5} \right)^2} = 16{x^2} \end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l} 4x \ge 0\\ {x^2}\left[ {{{\left( {x + 5} \right)}^2} - 16} \right] = 0 \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} x \ge 0\\ \left[ \begin{array}{l} {x^2} = 0\\ {\left( {x + 5} \right)^2} = 16 \end{array} \right. \end{array} \right.\\ \Leftrightarrow \left\{ \begin{array}{l} x \ge 0\\ \left[ \begin{array}{l} x = 0\\ x + 5 = 4\\ x + 5 = - 4 \end{array} \right. \end{array} \right. \Leftrightarrow \left\{ \begin{array}{l} x \ge 0\\ \left[ \begin{array}{l} x = 0\\ x = - 1\\ x = - 9 \end{array} \right. \end{array} \right. \Leftrightarrow x = 0 \end{array}$
