Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 14: Partial Derivatives - Section 14.5 - Directional Derivatives and Gradient Vectors - Exercises 14.5 - Page 826: 3

Answer

$$ \begin{array}{l} \nabla g=\left\langle g_x, g_y\right\rangle \\ g_x=y^2 \text { and } g_y=2 x y \text { so } \nabla_g=\left\langle y^2, 2 x y\right\rangle \end{array} $$ $$ \text { point }(2,1) \quad x=2 \quad y=1 \text { so } \nabla g=\langle 1,4\rangle $$

Work Step by Step

$$ Question \ says \ g(x,y)= xy^{2} \\ At \ point (2,-1) \ g(2,-1) =2 \\ so\\ xy^{2} =2\\ \text{ let's leave x alone to draw} \\ \text {the graph of level curce easily: }\\ x= \frac{2}{y^2}\\ \text{ Thus we can sketch gradient vector}\\ \text{ at initial point (2,-1) on the level curve} $$
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