Answer
$g(x) - f(x)$ or $(g-f)$
Work Step by Step
Notice that $(x+1)$, which is equal to function $f$, is subtracted to $x^3$, which is function $g$.
Thus,
$g(x)-f(x)=x^3-(x+1)$
Therefore, the missing expression in the given statement is:
$g(x) - f(x)$ or $g-f$.
