Answer
Not a real number
Work Step by Step
Based on the definition of $a^{\frac{m}{n}}$, we know that $a^{\frac{m}{n}}=(\sqrt[n] a)^{m}=\sqrt[n] a^{m}$ (where $\sqrt[n] a$ is a real number).
Therefore, $\sqrt[4] (-5)^{4}=(\sqrt[4] -5)^{4}$. We know that this cannot be a real number, as $\sqrt[4] -5$ is not real number, because there is no number $a$ such that $a^{4}=-5$.
