\( f(x)=\sqrt{x} \)
\( \frac{d f(x)}{d x}=\lim \limits_{h \rightarrow 0} \frac{\sqrt{x+h}-\sqrt{x}}{h}= \)
\( =\lim \limits_{h \rightarrow 0} \frac{(\sqrt{x+h}-\sqrt{x}) \cdot(\sqrt{x+h}+\sqrt{x})}{h \cdot(\sqrt{x+h}+\sqrt{x})}= \)
\( =\lim \limits_{h \rightarrow 0} \frac{x+h-x}{h \cdot(\sqrt{x+h}+\sqrt{x})}= \)
\( =\lim \limits_{h \rightarrow 0} \frac{h}{h \cdot(\sqrt{x+h}+\sqrt{x})}= \)
\( =\lim \limits_{h \rightarrow 0} \frac{1}{(\sqrt{x+h}+\sqrt{x})}= \)
\( =\frac{1}{2 \cdot \sqrt{x}} \)