Calculus, 10th Edition (Anton)

Published by Wiley
ISBN 10: 0-47064-772-8
ISBN 13: 978-0-47064-772-1

Chapter 13 - Partial Derivatives - 13.6 Directional Derivatives And Gradients - Exercises Set 13.6 - Page 969: 56

Answer

Vector along the gradient: $\frac{1}{2} \mathbf{i}=\mathbf{V}$ Unit vector: $\mathbf{i}=\mathbf{v}$ Rate of change: $\frac{1}{2}=\|\nabla f(0,2)\|$

Work Step by Step

$f$ Increases more quickly in positive direction of $\nabla f(x, y)$ \[ \begin{array}{l} \frac{y}{(x+y)^{2}}=f_{x}(x, y) \\ \frac{1}{2}=f_{x}(0,2) \\ -\frac{x}{(x+y)^{2}} =f_{y}(x, y) \\ 0=f_{y}(0,2) \end{array} \] \[ \nabla f(0,2)=\frac{1}{2} \mathbf{i} \] Vector along the gradient: $\frac{1}{2} \mathbf{i}=\mathbf{V}$ Unit vector: $\mathbf{i}=\mathbf{v}$ Rate of change: $\frac{1}{2}=\|\nabla f(0,2)\|$
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