Đề bài

Tìm x biết: a)      \({x^2} - 4x = 0\) b)      \(2{x^3} - 2x = 0\)

Lời giải chi tiết

a)\(\begin{array}{l}{x^2} - 4x = 0\\ \Leftrightarrow x\left( {x - 4} \right) = 0\\ \Leftrightarrow \left[ {\begin{array}{*{20}{c}}{x = 0}\\{x - 4 = 0}\end{array}} \right.\\ \Leftrightarrow \left[ {\begin{array}{*{20}{c}}{x = 0}\\{x = 4}\end{array}} \right.\end{array}\)Vậy \(x \in \left\{ {0;4} \right\}\)b)\(\begin{array}{l}2{x^3} - 2x = 0\\ \Leftrightarrow 2x\left( {{x^2} - 1} \right) = 0\\ \Leftrightarrow 2x\left( {x - 1} \right)\left( {x + 1} \right) = 0\\ \Leftrightarrow \left[ \begin{array}{l}x = 0\\x - 1 = 0\\x + 1 = 0\end{array} \right.\\ \Leftrightarrow \left[ \begin{array}{l}x = 0\\x = 1\\x =  - 1\end{array} \right.\end{array}\)Vậy \(x \in \left\{ {0;1; - 1} \right\}\)