Calculus 8th Edition

Published by Cengage
ISBN 10: 1285740629
ISBN 13: 978-1-28574-062-1

Chapter 16 - Vector Calculus - 16.8 Stokes' Theorem - 16.8 Exercises - Page 1179: 6

Answer

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Work Step by Step

Stokes' Theorem states that $\iint_{S} curl F \cdot dS=\iint_{C} F \cdot dr$ where, $C$ corresponds to the boundary of the surface oriented counter-clockwise. The boundary of the part of the ellipsoid $4x^2+y^2+4z^2=4$ is a circle $x^2+z^2=1$ and the parameterization of the boundary can be written as: $C: r(t)=\cos ti+0j+\sin t k$ and $dr=(-sin ti+0j +\cos t k) dt$ Now, $F[r(t)]=i+e^{(\cos t \ \sin t) } j+\cos^2 t \sin t k$ and $$\iint_{C} F \cdot dr =\int_0^{2 \pi} (i+e^{(\cos t \sin t)} j+\cos^2 t \sin t k) \cdot (-\sin t i+0 j+\cos t k) dt \\=\int_0^{2 \pi} -\sin t+\cos^3 t \sin t dt \\=\int_{0}^{2\pi} (1-\cos^3 t) \times (-\sin t dt)$$ Consider $cos t =p \implies -\sin t dt =dp$ Thus, $$\iint_{S} curl F \cdot dS=\iint_{C} F \cdot dr=\int_{1}^{1} (1-p^3) dp=0$$
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