ĐKXĐ: \(4-x^2>0\Rightarrow-2< x< 2\)
\(\Leftrightarrow\frac{x^3}{\sqrt{4-x^2}}=4-x^2=\sqrt{4-x^2}^2\)
\(\Leftrightarrow x^3=\left(\sqrt{4-x^2}\right)^3\)
\(\Leftrightarrow x=\sqrt{4-x^2}\) (\(x\ge0\))
\(\Leftrightarrow x^2=4-x^2\)
\(\Leftrightarrow x^2=2\Rightarrow x=\sqrt{2}\)