University Calculus: Early Transcendentals (3rd Edition)

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

Chapter 15 - Section 15.6 - Surface Integrals - Exercises - Page 884: 27

Answer

$$\dfrac{-73 \pi}{6} $$

Work Step by Step

$F \cdot n =\dfrac{-x^2 }{\sqrt {x^2+y^2}}-\dfrac{y^2 }{\sqrt {x^2+y^2}} -x^2-y^2$ Now, $I=\iint_{S} F \cdot n \ dS=\iint_{R} [\dfrac{-x^2 }{\sqrt {x^2+y^2}}-\dfrac{y^2 }{\sqrt {x^2+y^2}} -x^2-y^2] \ dy \ dx \\=-\int_0^{2 \pi} \int_{1}^{2} [\dfrac{r^2 }{\sqrt {r^2}} \times \cos^2 \theta+\dfrac{r^2)}{(\sqrt {r^2}} \times \sin^2 \theta+r^2 \cos^2 \theta +r^2 \sin^2 \theta] (r \ dr) d \theta \\=-\int_0^{2 \pi} \int_{1}^{2} (r^2+r^3) r dr d \theta \\= -\int_0^{2 \pi} [\dfrac{1}{3} r^3 +\dfrac{1}{4} r^4]_1^2 \ d \theta \\=\dfrac{-73 \pi}{6} $
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