5. The solution to the equation $\frac{x^{3}}{\sqrt{4-x^{2}}}+x^{2}-4=0$ is $\qquad$
5. $\sqrt{2}$, (Hint: Transform the equation to $x^{3}=\left(4-x^{2}\right)$ - $\sqrt{4-x^{2}}$, then take the cube root of both sides and square them, resulting in $x= \pm \sqrt{2}$, but $x=-\sqrt{2}$ is an extraneous root and should be discarded.)