\(\left(x^2-5\right)\left(x^2-25\right)=0\)
\(\Rightarrow\orbr{\begin{cases}x^2-5=0\\x^2-25=0\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x^2=5\\x^2=25\end{cases}}\)
\(\Rightarrow\orbr{\begin{cases}x\in\left\{-\sqrt{5};\sqrt{5}\right\}\\x\in\left\{5;-5\right\}\end{cases}}\)
Vậy \(x\in\left\{-5;-\sqrt{5};\sqrt{5};5\right\}\)