Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 4: Applications of Derivatives - Section 4.4 - Concavity and Curve Sketching - Exercises 4.4 - Page 214: 89

Answer

See graph and explanations.

Work Step by Step

Step 1. Identify the domain of the function: rewrite the function as $y=\frac{x}{x^2-1}=\frac{1}{2(x+1)}+\frac{1}{2(x-1)}$ (this decomposition is easy to see backwards); we can identify the domain as $(-\infty,-1)\cup(-1,1)\cup (1,\infty)$. Step 2. Take derivatives to get $y'=-\frac{1}{2(x+1)^2}-\frac{1}{2(x-1)^2}$ and $y''=\frac{1}{(x+1)^3}+\frac{1}{(x-1)^3}$. Step 3. We can find the possible critical points as $x=\pm1$. Check the signs of $y'$ across the critical points: $..(-)..(-1)..(-)..(1)..$; thus the function decreases on $(-\infty, -1),(-1,1),(1,\infty)$,and there are no extrema. Step 4. Check concavity across $x=0,\pm1$ with signs of $y''$:$..(-)..(-1)..(+)..(0)..(-)..(1)..(+)..$; thus the function is concave down on $(-\infty,-1), (0,1)$ and concave up on $(-1,0),(1,\infty)$, and $x=0$ is an inflection point. Step 5. We can identify a vertical asymptote as $x=\pm1$, and a horizontal asymptote as $y=0$. Step 6. The y-intercepts can be found by letting $x=0$ to get $y(0)=0$. Step 7. Based on the above results, we can graph the function as shown in the figure.
Update this answer!

You can help us out by revising, improving and updating this answer.

Update this answer

After you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.