Calculus 8th Edition

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

Chapter 14 - Partial Derivatives - 14.6 Directional Derivatives and the Gradient Vector - 14.6 Exercises - Page 999: 59

Answer

$\dfrac{-5}{4}, \dfrac{-5}{4},\dfrac{25}{8}$

Work Step by Step

Our aim is to determine the normal line equation. The general form is: $\dfrac{(x_2-x_1)}{f_x(x_1,y_1,z_1)}=\dfrac{(y_2-y_1)}{f_y(x_1,y_1,z_1)}=\dfrac{(z_2-z_1)}{f_x(x_1,y_1,z_1)}$ ...(1) From the given data, we have $f(x,y,z)=(1,1,2)$ Equation (1), becomes: Thus, $\dfrac{(x-1)}{2}=\dfrac{(y-1)}{2}=\dfrac{(z-2)}{-1}$ Consider $\dfrac{(x-1)}{2}=\dfrac{(y-1)}{2}=\dfrac{(z-2)}{-1}=s$ Therefore, $x=1+3s;y=1+2s,z=2-s$ Simplify to get the value of $s$, we have $s=-\dfrac{9}{8}$ Equation of a paraboloid is: $z=x^2+y^2$ This yields $x=\dfrac{-5}{4},y=\dfrac{-5}{4},z=\dfrac{25}{8}$
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