\(x^2\ge4\Leftrightarrow\left[{}\begin{matrix}x\ge2\\x\le-2\end{matrix}\right.\) vậy ......................
\(x^2\ge4\)
\(\Leftrightarrow x^2-4\ge0\)
\(\Leftrightarrow\left(x-2\right)\left(x+2\right)\ge0\)
TH 1 : \(\left(x-2\right)\left(x+2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)
TH 2 : \(\left(x-2\right)\left(x+2\right)>0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-2>0\\x+2>0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x>2\\x>-2\end{matrix}\right.\)
\(\Leftrightarrow x>2\)
Vậy ...
