Toán Lớp 8: Tìm x, biết: a) x3 – 9x = 0 b) x(2x – 7) – 4x + 14 = 0
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{x^3}–9x = 0\\
\Rightarrow x\left( {{x^2} – 9} \right) = 0\\
\Rightarrow x\left( {x – 3} \right)\left( {x + 3} \right) = 0\\
\Rightarrow \left[ \begin{array}{l}
x = 0\\
x – 3 = 0\\
x + 3 = 0
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
x = 0\\
x = 3\\
x = – 3
\end{array} \right.\\
x\left( {2x–7} \right)–4x + 14 = 0\\
\Rightarrow x(2x – 7) – 2(2x – 7) = 0\\
\Rightarrow (x – 2)(2x – 7) = 0\\
\Rightarrow \left[ \begin{array}{l}
x – 2 = 0\\
2x – 7 = 0
\end{array} \right. \Rightarrow \left[ \begin{array}{l}
x = 2\\
x = \frac{7}{2}
\end{array} \right.
\end{array}\]