Answer
2x
Work Step by Step
$\lim\limits_{h \to 0}\frac{(x + h)^{2}-x^{2}}h = \lim\limits_{h \to 0}\frac{(x+h-x)(x+h+x)}{h}= \lim\limits_{h \to 0} \frac{h(2x +h)}{h}=2x$
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