Problems with finding limit The function $f(x)$ has a derivative at the point $a$ and  $f(a) > 0$. I need to find the limit as n $\to + \infty$ of $$\left(\frac{f(a + \frac1n)}{f(a)} \right)^n$$ Substitution method?

By definition of derivative we get 
$$ \lim_{n\to \infty}\left(\frac{f(a + \frac1n)}{f(a)} \right)^n= \lim_{n\to \infty}
\exp\left[n\log\left(\frac{f(a+1/n)}{f(a)}\right )\right]
=\lim_{h\to 0}\exp\left[\frac{\log\left(f(a+h\right ) -\log f(a)}{h}\right] =\exp\left(\frac{f'(a)}{f(a)}\right)$$
