Answer
$\frac{f(x)-f(a)}{x-a}=(x+a)(x^2+a^2)$
Work Step by Step
$f(x) = x^4$
$\frac{f(x)-f(a)}{x-a}=\frac{x^4-a^4}{x-a} = \frac{(x^2-a^2)(x^2+a^2)}{(x-a)} =\frac{(x-a)(x+a)(x^2+a^2)}{(x-a)}=\frac{(x+a)(x^2+a^2)}{1}=(x+a)(x^2+a^2)$
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