University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 2 - Section 2.3 - The Precise Definition of a Limit - Exercises - Page 78: 60

Answer

(a) Let $\epsilon=0.5$ then prove that for $x\lt-1$, $|g(x)-2|\ge\epsilon$. (b) $\lim_{x\to-1}g(x)$ does appear to exist, and it equals $1$.

Work Step by Step

(a) $\lim_{x\to-1}g(x)\ne2$ We need to choose a $\epsilon\gt0$, then prove that for each $\delta\gt0$, there exists a value of $x$ such that $$0\lt|x-(-1)|\lt\delta\Rightarrow|g(x)-2|\ge\epsilon$$ - Let $\epsilon=0.5$ - Looking at the graph, for $x\lt-1$, $g(x)\lt-1$ This means $g(x)-2\lt-1-2=-3$ Therefore, $|g(x)-2|\gt3\gt0.5$ Hence, $\lim_{x\to-1}g(x)\ne2$ according to limit definition. (b) $\lim_{x\to-1}g(x)$ does appear to exist, and it equals $1$. Because if we choose an arbitrary $\epsilon\gt0$ and let the value of $g(x)$ fluctuate between $1-\epsilon$ and $1+\epsilon$, we can always find a corresponding value of $\delta\gt0$ and the corresponding values of $x$ would be restricted in the interval $(-1-\delta,-1+\delta)$. In other words, $$0\lt|x-(-1)|\lt\delta\Rightarrow|g(x)-1|\lt\epsilon$$
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