Evaluating the limit $\lim_{h\to 0} \frac{\sqrt {1 - (x+h) ^2} - \sqrt {1-x^2}} {h}$ Find the limit
$\lim_{h\to 0} \frac{\sqrt {1 - (x+h) ^2} - \sqrt {1-x^2}} {h}$
I tried substituting "h" and also multiplying $\frac{\sqrt {1 - (x+h) ^2} + \sqrt {1-x^2}}{\sqrt {1 - (x+h) ^2} + \sqrt {1-x^2}}$

Let $f(x)=\sqrt{1-x^2}$
$$f'(x)=\lim_{h \to 0}\frac{\sqrt{1-({x+h})^2}-\sqrt{1-x^2}}{h}=\frac{-x}{\sqrt{1-x^2}}$$
