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: 60

Answer

$(-7,-2,-7); (\dfrac{19}{3}, \dfrac{14}{3},\dfrac{19}{3})$

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 $f(x,y,z)=(1,2,1)$ Equation (1), becomes: Thus, $\dfrac{(x-1)}{8}=\dfrac{(y-2)}{4}=\dfrac{(z-1)}{8}$ Let us consider $\dfrac{(x-1)}{8}=\dfrac{(y-2)}{4}=\dfrac{(z-1)}{8}=s$ Therefore, $x=1+8s;y=2+4s,z=1+8s$ After simplifications we get $s=-1,\dfrac{2}{3}$ $x=-7,y=-2,z=-7;$ or, $x=\dfrac{19}{3}, y=\dfrac{14}{3},z=\dfrac{19}{3}$ Therefore, the normal line through the point (1,2,1) on the ellipsoid intersect the sphere $x^2+y^2+z^2=102$ are: $(-7,-2,-7); (\dfrac{19}{3}, \dfrac{14}{3},\dfrac{19}{3})$
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