University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 2 - Section 2.6 - Limits Involving Infinity; Asymptotes of Graphs - Exercises - Page 108: 32

Answer

$$\lim_{x\to-\infty}\frac{\sqrt[3]x-5x+3}{2x+x^{2/3}+4}=-\frac{5}{2}$$

Work Step by Step

We would treat these exercises just like we treat the limits of rational functions: we would divide both numerator and denominator by the highest power of $x$ in the denominator. Also remember that $$\lim_{x\to\infty}\frac{a}{x^n}=\lim_{x\to-\infty}\frac{a}{x^n}=a\times0=0\hspace{1cm}(a\in R)$$ $$A=\lim_{x\to-\infty}\frac{\sqrt[3]x-5x+3}{2x+x^{2/3}+4}=\lim_{x\to-\infty}\frac{x^{1/3}-5x+3}{2x+x^{2/3}+4}$$ The highest power of $x$ in the denominator here is $x$, so we divide both numerator and denominator by $x$: $$A=\lim_{x\to-\infty}\frac{x^{-2/3}-5+\frac{3}{x}}{2+x^{-1/3}+\frac{4}{x}}=\lim_{x\to-\infty}\frac{\frac{1}{x^{2/3}}-5+\frac{3}{x}}{2+\frac{1}{x^{1/3}}+\frac{4}{x}}$$ $$A=\frac{0-5+0}{2+0+0}=-\frac{5}{2}$$
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