University Calculus: Early Transcendentals (3rd Edition)

Published by Pearson
ISBN 10: 0321999584
ISBN 13: 978-0-32199-958-0

Chapter 2 - Section 2.2 - Limit of a Function and Limit Laws - Exercises - Page 68: 71

Answer

$$\lim_{x\to-1}f(x)=2$$

Work Step by Step

$$f(x)=\frac{x^2-1}{|x|-1}$$ (a) The table is shown below. As we can see from 2 tables below, as $x$ gets more decimals and approaches $-1$, the value of $f(x)$ also gets more decimals and apparently approaches $2$. So I would estimate here that $\lim_{x\to-1}f(x)=2$. (b) The graph is shown below. Again, looking at the graph, the closer $x$ approaches $-1$, the closer $f(x)$ approaches $2$. (c) $$\lim_{x\to-1}f(x)=\lim_{x\to-1}\frac{x^2-1}{|x|-1}$$ For $x\ge0$, $|x|=x$ and for $x\lt0$, $|x|=-x$ However, here we need to calculate the limit of $f(x)$ as $x\to-1$, and we care only the values of $x$ very close around $-1$. So we can say here that we choose $x\lt0$, and $|x|=-x$ $$\lim_{x\to-1}f(x)=\lim_{x\to-1}\frac{x^2-1}{-x-1}=\lim_{x\to-1}\frac{(x-1)(x+1)}{-(x+1)}$$ $$\lim_{x\to-1}f(x)=\lim_{x\to-1}\frac{x-1}{-1}=1-x=1-(-1)=2$$ Therefore, $$\lim_{x\to-1}f(x)=2$$
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