Lời giải:
Để căn thức có nghĩa thì \(4-x^2\geq 0\Leftrightarrow (2-x)(2+x)\geq 0\)
\(\Leftrightarrow \left[\begin{matrix} \left\{\begin{matrix} 2-x\geq 0\\ 2+x\geq 0\end{matrix}\right.\\ \left\{\begin{matrix} 2-x\leq 0\\ 2+x\leq 0\end{matrix}\right.\end{matrix}\right.\)
\(\Leftrightarrow \left[\begin{matrix} \left\{\begin{matrix} x\leq 2\\ x\geq -2\end{matrix}\right.\\ \left\{\begin{matrix} x\geq 2\\ x\leq -2\end{matrix}\right.(\text{vô lý})\end{matrix}\right.\)
\(\Rightarrow \left\{\begin{matrix} x\leq 2\\ x\geq -2\end{matrix}\right.\) hay \(-2\leq x\leq 2\)