Calculus: Early Transcendentals 8th Edition

Published by Cengage Learning
ISBN 10: 1285741552
ISBN 13: 978-1-28574-155-0

Chapter 14 - Section 14.8 - Lagrange Multipliers - 14.8 Exercise - Page 977: 8

Answer

Maximum:$f(2,2\sqrt2,2 \sqrt2)=e^{16}$, Minimum: $f(-2,-2\sqrt2,-2 \sqrt2)=e^{-16}$ or, Maximum:$f(2,\sqrt8, \sqrt 8)=e^{16}$, Minimum: $f(-2,-\sqrt 8,-\sqrt 8)=e^{-16}$

Work Step by Step

Use Lagrange Multipliers Method: $\nabla f(x,y,z)=\lambda \nabla g(x,y,z)$ This yields $\nabla f=\lt yze^{xyz},xze^{xyz},xye^{xyz} \gt$ and $\lambda \nabla g=\lambda \lt 4x,2y,2z\gt$ Using the constraint condition $2x^2+y^2+z^2=24$ we get, $yze^{xyz}=\lambda 4x, xze^{xyz}=\lambda 2y,xye^{xyz}=\lambda 2z$ After solving, we get $y=z=2x^2$ Since, $g(x,y)=2x^2+y^2+z^2=24$ gives $x=\pm 2$ Thus, $y=z=\pm 2\sqrt2$ Hence, Maximum:$f(2,2\sqrt2,2 \sqrt2)=e^{16}$, Minimum: $f(-2,-2\sqrt2,-2 \sqrt2)=e^{-16}$ or, Maximum:$f(2,\sqrt8, \sqrt 8)=e^{16}$, Minimum: $f(-2,-\sqrt 8,-\sqrt 8)=e^{-16}$
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