Proof derivative equals zero?
Solution 1:
Taking the derivative with respect to $h$ gives:
$$f'(x) = \lim_{h \rightarrow 0} \frac{f'(x + h)}{1}$$
Since $f(x)$ is constant with respect to $h$.
Solution 2:
You differentiated the numerator with respect to $x$ but the denominator with respect to $h$.