University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 15 - Section 15.5 - Surfaces and Area - Exercises - Page 873: 45

Answer

$\dfrac{\pi}{6}(17\sqrt {17}-5\sqrt {5}) $

Work Step by Step

Here, we have $r_r=( \cos \theta) i+(\sin \theta) j+2k$ and $r_{\theta}=(-r\sin \theta) i+( r\cos \theta) j$ Also, $|r_r \times r_{\theta}|=r\sqrt {4r^2+1}$ Thus, the area is given by $A=\int_0^{2 \pi} \int_1^{2} (r\sqrt {4r^2+1}) dr d \theta$ or, $A=\int_0^{2 \pi} (\dfrac{17\sqrt {17}}{12}- \dfrac{5\sqrt {5}}{12}-)d \theta= \dfrac{\pi}{6}(17\sqrt {17}-5\sqrt {5}) $
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