# Chapter 2 - Differentiation - 2.1 Exercises: 18

$f'(x)=2x$

#### Work Step by Step

To take the derivative of a function using the limit process, plug into the equation $f'(x)=\lim\limits_{h \to 0}\frac{f(x+h)-f(x)}{h}$ and simplify: $f'(x)=\lim\limits_{h \to 0}\frac{[(x+h)^2-5]-(x^2-5)}{h}$ $f'(x)=\lim\limits_{h \to 0}\frac{x^2+2xh+h^2-5-x^2+5}{h}$ $f'(x)=\lim\limits_{h \to 0}\frac{2xh+h^2}{h}$ $f'(x)=\lim\limits_{h \to 0}2x+h$ Once you can't simplify any further, plug $0$ in for $h$. $f'(x)=2x+(0)=2x$

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