If $f(x) = \sqrt{x^{2} + 9}$, what is $f'\left(4\right)$?

Explanation

1. 01

   $f'(x) = \frac{2x}{2\sqrt{x^{2} + 9}} = \frac{x}{\sqrt{x^{2} + 9}}$.

2. 02

   At 4: $\frac{4}{5}$.