Answer
Fill the blanks with
... $x$ ... $(g\circ f)(x)$ ..
Work Step by Step
Let $f$ be a one-to-one function.
Then $g$ is the inverse function of $f$ if
$(f\circ g)(x)=x$ for every $x$ in the domain of $g$,
and $(g\circ f)(x)=x$ for every $x$ in the domain of $f$.
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Fill the blanks with
... $x$ ... $(g\circ f)(x)$ ...
