Find the directional derivative of f(x, y, z) = -4x? + ly? – 4z2 at the point (0, -4, 2) in the direction of the origin.

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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Find the directional derivative of f(x, y, z) = -4x? + ly? – 4z2 at the point (0, -4, 2) in the direction of the origin.
Transcribed Image Text:Find the directional derivative of f(x, y, z) = -4x? + ly? – 4z2 at the point (0, -4, 2) in the direction of the origin.
Expert Solution
Step 1

Given function

f(x,y, z) = -4x +ly² – 4z²
Step 2
The directional derivative of function fat the point (x.y.z) in the direction of unit vector 'u' is
given by
3(a,b,c)
Df (x,y, z) = f,(x,y, z)a+ f,(x, y,z)b+ f¿(x, y,z)c
Step 3
Now,
Differentiate the given function partially using Power rule:
(x*) = a·x
Power Rule:
de
Therefore,
Differentiating partially with respect to x, we get
8f
:-8x +0-0
8x
f =-8x
Differentiating partially with respect to y, we get
8f
= 0+2y –0
f, = 2y
Differentiating partially with respect to z, we get
of
=0+0-8z
8z
f, =-8z
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