Answer
$$ (x^4+3x^2)(\sqrt{x-1})$$
Work Step by Step
In order to simplify the expression, we first simplify each of the terms, and then we combine like terms. Doing this, we find:
$$ \sqrt[4]{x^5-x^4}+3\sqrt[4]{x^9-x^8}\\ x\sqrt[4]{x-1}+3x^2\sqrt[4]{x-1} \\ (x^4+3x^2)(\sqrt{x-1})$$
