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: 29

Answer

$\lim_{x\to-4}\dfrac{\dfrac{1}{4}+\dfrac{1}{x}}{4+x}=-\dfrac{1}{16}$

Work Step by Step

$\lim_{x\to-4}\dfrac{\dfrac{1}{4}+\dfrac{1}{x}}{4+x}$ Try to evaluate the limit applying direct substitution: $\lim_{x\to-4}\dfrac{\dfrac{1}{4}+\dfrac{1}{x}}{4+x}=\dfrac{\dfrac{1}{4}+\dfrac{1}{-4}}{4-4}=\dfrac{0}{0}$ Indeterminate form The limit could not be evaluated using direct substitution. Evaluate the sum of fractions in the numerator and simplify: $\lim_{x\to-4}\dfrac{\dfrac{1}{4}+\dfrac{1}{x}}{4+x}=\lim_{x\to-4}\dfrac{\dfrac{4+x}{4x}}{4+x}=\lim_{x\to-4}\dfrac{4+x}{4x(4+x)}=...$ $...=\lim_{x\to-4}\dfrac{1}{4x}=...$ Try to evaluate the limit using direct substitution again: $...=\lim_{x\to-4}\dfrac{1}{4x}=\dfrac{1}{4(-4)}=-\dfrac{1}{16}$
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