Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 3 - Applications of Differentiation - 3.4 Limits at Infinity; Horizontal Asymptotes - 3.4 Exercises - Page 242: 35

Answer

$$ y= \frac{5+4 x}{x+3} $$ We obtain that: $y = 4$ is a horizontal asymptote. $x=-3$ is a vertical asymptote. The graph confirms our work.

Work Step by Step

$$ y= \frac{5+4 x}{x+3} $$ we calculated that $$ \lim _{x \rightarrow \pm \infty} \frac{5+4 x}{x+3} $$ we divide the numerator and denominator by the highest power of $x$ in the denominator, which is just $x$: $$ \begin{aligned} \lim _{x \rightarrow \pm \infty} \frac{5+4 x}{x+3}& =\lim _{x \rightarrow \pm \infty} \frac{(5+4 x) / x}{(x+3) / x}\\ &=\lim _{x \rightarrow \pm \infty} \frac{5 / x+4}{1+3 / x} \\ &=\frac{0+4}{1+0} \\ &=4 \end{aligned} $$ so, $y = 4$ is a horizontal asymptote. $$ y=f(x)= \frac{5+4 x}{x+3}, $$ so, $$ \lim _{x \rightarrow -3^{+}}f(x)=-\infty $$ since $$ 5+4 x \rightarrow-7 \text { and } x+3 \rightarrow 0^{+} \text {as } x \rightarrow-3^{+} $$ and, $$ \lim _{x \rightarrow -3^{-}}f(x)=\infty $$ since $$ 5+4 x \rightarrow-7 \text { and } x+3 \rightarrow 0^{-} \text {as } x \rightarrow-3^{-} $$ Thus $x=-3$ is a vertical asymptote. The graph confirms our work.
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