a) \(\left(x^2-4\right)\left(x^2-9\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x^2-4=0\\x^2-9=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x^2=2^2\\x^2=3^2\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\pm2\\x=\pm3\end{matrix}\right.\)
b) \(\left(x^2-4\right)\left(x^2-9\right)\le0\)
\(\Rightarrow\left[{}\begin{matrix}x^2-4\ge0;x^2-9\le0\\x^2-4\le0;x^2-9\ge0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x^2\ge4;x^2\le9\\x^2\le4;x^2\ge9\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}4\le x^2\le9\left(tm\right)\\9\le x^2\le4\left(loại\right)\end{matrix}\right.\)
\(\Rightarrow x^2\in\left\{4;5;...;9\right\}\)
\(\Rightarrow x\in\left\{\pm2;\pm\sqrt{5};...;\pm3\right\}\).
a) ( x2 - 4 ) . ( x2 - 9 ) = 0
=> \(\left[{}\begin{matrix}x^2-4=0\\x^2-9=0\end{matrix}\right.=>\left[{}\begin{matrix}x^2=4\\x^2=9\end{matrix}\right.\)
= > \(\left[{}\begin{matrix}x=-2\\x=2\\x=3\\x=-3\end{matrix}\right.\)
