Answer
$$2x $$
Work Step by Step
\begin{align*}
\lim _{h \rightarrow 0} \frac{(x+h)^{2}-x^{2}}{h}&=\lim _{h \rightarrow 0} \frac{\left(x^{2}+2 h x+h^{2}\right)-x^{2}}{h}\\
&=\lim _{h \rightarrow 0}(2 x+h)\\
&=2 x
\end{align*}
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