Calculus: Early Transcendentals 9th Edition

Published by Cengage Learning
ISBN 10: 1337613924
ISBN 13: 978-1-33761-392-7

Chapter 2 - Section 2.6 - Limits at Infinity; Horizontal Asymptotes - 2.6 Exercises - Page 139: 59

Answer

(a) $f(0) = \frac{5}{4}$ (b) $\lim\limits_{x \to \infty}f(x) = 5$

Work Step by Step

$(x-4)$ is a term in the denominator since $x=4$ is a vertical asymptote. $(x-1)$ is a term in the numerator since $x=1$ is an x-intercept. $(x+1)$ is a term in both the numerator and the denominator since there is a removable discontinuity at $x = -1$ We can write the function $f$: $f(x) = \frac{c~(x-1)~(x+1)}{(x-4)(x+1)}$ where $c$ is a constant $\lim\limits_{x \to -1}f(x) = \frac{c~[(-1)-1]}{(-1)-4} = \frac{2c}{5} = 2$ Thus, $c = 5$ We can write the function $f$: $f(x) = \frac{5~(x-1)~(x+1)}{(x-4)(x+1)}$ (a) We can find $f(0)$: $f(0) = \frac{5~(0-1)~(0+1)}{(0-4)(0+1)} = \frac{5}{4}$ (b) We can find $\lim\limits_{x \to \infty}f(x)$: $\lim\limits_{x \to \infty}f(x) = \lim\limits_{x \to \infty}\frac{5~(x-1)~(x+1)}{(x-4)(x+1)} = \lim\limits_{x \to \infty}\frac{5~(x^2-1)}{x^2-3x-4} = 5$
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