Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

Chapter 2 - Section 2.6 - Rational Functions and Their Graphs - Exercise Set - Page 399: 88

Answer

a) The slant asymptote of the given function is $y=x-9$. b) The graph of the function is shown below as:

Work Step by Step

(a) Consider the rational function $f\left( x \right)=\frac{{{x}^{3}}-1}{{{x}^{2}}-9}$. Here, the degree of the numerator term is 2 and degree of the denominator term is 1. And $x=0$ does not constitute a factor of the function ${{x}^{3}}-1$ , so, the graph of the function has a slant asymptote. Now, divide the function ${{x}^{3}}-1$ with ${{x}^{2}}-9$. $\frac{{{x}^{3}}-1}{{{x}^{2}}-9}=x+\frac{13}{3\left( x-3 \right)}+\frac{14}{3\left( x+3 \right)}$ Therefore, the equation has a slant asymptote at $y=x-9$. (b) Consider the rational function $f\left( x \right)=\frac{{{x}^{3}}-1}{{{x}^{2}}-9}$. Here, the degree of the numerator term is 2 and degree of the denominator term is 1. And $x=0$ does not constitute factor of the function ${{x}^{3}}-1$ , so, the graph of the function has a slant asymptote. Determine the symmetry. $f\left( x \right)=\frac{{{x}^{3}}-1}{{{x}^{2}}-9}$ Substitute $x=-x$ and then, $\begin{align} & f\left( -x \right)=\frac{{{\left( -x \right)}^{3}}-1}{{{\left( -x \right)}^{2}}-9} \\ & =\frac{-{{x}^{3}}-1}{{{x}^{2}}-9} \end{align}$ The graph is not symmetrical about the $y$ axis. Compute the $y$ intercept. Put $x=0$ $\begin{align} & f\left( x \right)=\frac{{{x}^{3}}-1}{{{x}^{2}}-9} \\ & f\left( 0 \right)=\frac{{{\left( 0 \right)}^{3}}-1}{{{\left( 0 \right)}^{2}}-9} \\ & =\frac{1}{9} \end{align}$ The $y$ intercept is $y=\frac{1}{9}$. Compute the $x$ intercept. Put $p\left( x \right)=0$ and then, $\begin{align} & {{x}^{3}}-1=0 \\ & {{x}^{3}}=1 \\ & =\sqrt[3]{1} \\ & =1 \end{align}$ The $x$ intercept is $x=1$. Now, compute the vertical asymptotes. Set $q\left( x \right)=0$ $\begin{align} & {{x}^{2}}-9=0 \\ & x=3,-3 \end{align}$ Thus, the graph has a vertical asymptote as $x=3$ and $x=-3$. Determine the horizontal asymptotes. There is no horizontal asymptote because the degree of the numerator term is not equal to the degree of the denominator term.
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