Multivariable Calculus, 7th Edition

Published by Brooks Cole
ISBN 10: 0-53849-787-4
ISBN 13: 978-0-53849-787-9

Chapter 14 - Partial Derivatives - 14.8 Exercises - Page 987: 5

Answer

Maximum:$f(0,-1)=f(0,1)=1$, Minimum: $f(-2,0)=f(2,0)=-4$

Work Step by Step

Use Lagrange Multipliers Method: $\nabla f(x,y)=\lambda \nabla g(x,y)$ This yields $\nabla f=\lt y,x \gt$ and $\lambda \nabla g=\lambda \lt 8x,2y \gt$ Using the constraint condition $4x^2+y^2=8$ we get, $y=\lambda 8x, x=\lambda 2y$ After solving, we get $x=\pm 1$ Since, $g(x,y)=x^2+y^2=10$ gives $y=2$ Hence, Maximum:$f(0,-1)=f(0,1)=1$, Minimum: $f(-2,0)=f(2,0)=-4$
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