##### Hint

For this part, don't use the expressions you calculated for $f(x)$ and $g(x)$. We want the formula to involve just the symbols $f(x)$, $g(x)$, $\diff{f}{x}$ and $\diff{g}{x}$.

Online to enter derivatives like $\diff{f}{x}$, type `df/dx` or `f'(x)`.

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