Answer
Fill the blank with $x^{\frac{1}{4}}$.
Work Step by Step
With substitution $u=x^{\frac{1}{4}}$, and $x^{\frac{1}{2}}=u^{2}$. The equation becomes
$u-u^{2}-2=0$.
Multiply both sides by $-1$ to get
$u^{2}-u-2=0$.
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