Để F(x)=0 thì \(x^3-4x=0\)
\(\Leftrightarrow x\left(x^2-4\right)=0\)
\(\Leftrightarrow x\left(x-2\right)\left(x+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x-2=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=2\\x=-2\end{matrix}\right.\)
Vậy: \(x\in\left\{-2;0;2\right\}\)
\(f\left(x\right)=x^3-4x.\)
Để \(f\left(x\right)=0.\)
\(\Leftrightarrow x^3-4x=0\)
\(\Rightarrow x.\left(x^2-4\right)=0\)
\(\Rightarrow x.\left(x^2-2^2\right)=0\)
\(\Rightarrow x.\left(x-2\right).\left(x+2\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=0\\x-2=0\\x+2=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=0+2\\x=0-2\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\left(TM\right)\\x=2\left(TM\right)\\x=-2\left(TM\right)\end{matrix}\right.\)
Vậy \(x\in\left\{0;2;-2\right\}\) thì \(f\left(x\right)=0.\)
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