Precalculus: Mathematics for Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 1305071751
ISBN 13: 978-1-30507-175-9

Chapter 13 - Section 13.2 - Finding Limits Algebraically - 13.2 Exercises - Page 913: 35

Answer

$\lim_{x\to-1}\dfrac{x^{2}-x-2}{x^{3}-x}=-\dfrac{3}{2}$ The graph is shown below:

Work Step by Step

$\lim_{x\to-1}\dfrac{x^{2}-x-2}{x^{3}-x}$ Try to evaluate the limit applying direct substitution: $\lim_{x\to-1}\dfrac{x^{2}-x-2}{x^{3}-x}=\dfrac{(-1)^{2}-(-1)-2}{(-1)^{3}-(-1)}=\dfrac{0}{0}$ Indeterminate form The limit could not be evaluated using direct substitution. Factor the numerator and the denominator of the function and simplify: $\lim_{x\to-1}\dfrac{x^{2}-x-2}{x^{3}-x}=\lim_{x\to-1}\dfrac{(x-2)(x+1)}{x(x^{2}-1)}=...$ $...=\lim_{x\to-1}\dfrac{(x-2)(x+1)}{x(x-1)(x+1)}=\lim_{x\to-1}\dfrac{x-2}{x(x-1)}=...$ Try to evaluate the limit using direct substitution again: $\lim_{x\to-1}\dfrac{x-2}{x(x-1)}=\dfrac{-1-2}{(-1)(-1-1)}=\dfrac{-3}{(-1)(-2)}=-\dfrac{3}{2}$
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