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 4.5 - Applied Optimization - Exercises 4.5 - Page 224: 27

Answer

$h=1m$, $r=\sqrt 2m$ and $V=\frac{2\pi}{3}m^3$

Work Step by Step

Step 1. Using the Pythagorean Theorem, we have $h^2+r^2=3$ or $r^2=3-h^2$. Step 2. The volume of the cone is given by $V=\frac{1}{3}\pi r^2 h=\frac{1}{3}\pi (3-h^2) h=\frac{1}{3}\pi (3h-h^3)$ Step 3. $V'=\frac{1}{3}\pi (3-3h^2)$; let $V'=0$ to get $h=1m$; thus $r=\sqrt 2m$ and $V=\frac{1}{3}\pi (3-1^3)=\frac{2\pi}{3}m^3$ Step 4. Check $V''=\frac{1}{3}\pi (-6h)\lt0$ and the region is concave down with a maximum volume.
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