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 872: 17

Answer

$\dfrac{\pi \sqrt 5}{2}$

Work Step by Step

Here, we have $y+2z=2$ and $x^2+y^2=1$ Thus, $x=r \cos \theta, y=r \sin \theta $ $y+2z=2 \implies z=(\dfrac{2-r \sin \theta}{2})$ Then, we have $r(r,\theta)=(r \cos \theta) i+(r \sin \theta) j+(\dfrac{2-r \sin \theta}{2}) k$ Then $r_r=( \cos \theta) i+(\sin \theta) j-(\dfrac{ \sin \theta}{2}) k$ and $r_{\theta}=(-r \sin \theta) i+(r \cos \theta) j-(\dfrac{r \cos \theta}{2}) k$ Also, $|r_r \times rr_{\theta}|=\dfrac{\sqrt 5r}{2}$ where $0 \le r \le 1$; $0 \le \theta \le 2\pi$ Thus, the area is given by $A=\int_0^{2 \pi} \int_0^{1} \dfrac{\sqrt 5r}{2} dr d \theta$ or, $A=\int_0^{2 \pi} [ \dfrac{\sqrt 5r^2}{4}]_0^{1} d \theta=\dfrac{\pi \sqrt 5}{2}$
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