Let ū = (u1, u2) be a unit vector in R? and let f: R² → R be defined by if (x, y) # (0, 0), f (x, y) = x² + y? if (x, y) = (0, 0). (a) Find Daf(0, 0). (b) Using your solution to (a), find Vf(0,0). (c) Use the Lagrange multipliers algorithm to find the maximum and minimum directional derivatives at (0, 0). [Hint: What are you trying to optimize? What is the constraint?]

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter8: Applications Of Trigonometry
Section8.3: Vectors
Problem 60E
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Let ū = (u1, u2) be a unit vector in R? and let f: R² → R be defined by
x²y
x2 + y?
if (x, y) # (0, 0),
f (x, y) =
if (x, y) = (0,0).
(a) Find Daf(0, 0).
(b) Using your solution to (a), find Vf(0,0).
(c) Use the Lagrange multipliers algorithm to find the maximum and minimum directional
derivatives at (0,0). [Hint: What are you trying to optimize? What is the constraint?]
(d) If you've solved (b) and (c) correctly, you will have found that the maximum and mini-
mum directional derivatives are not equal to ||Vf(0,0)|| and –||Vf(0,0)||. This appears
to contradict the Greatest Rate of Change Theorem given in Unit 7.2. What went wrong?
Explain.
Transcribed Image Text:Let ū = (u1, u2) be a unit vector in R? and let f: R² → R be defined by x²y x2 + y? if (x, y) # (0, 0), f (x, y) = if (x, y) = (0,0). (a) Find Daf(0, 0). (b) Using your solution to (a), find Vf(0,0). (c) Use the Lagrange multipliers algorithm to find the maximum and minimum directional derivatives at (0,0). [Hint: What are you trying to optimize? What is the constraint?] (d) If you've solved (b) and (c) correctly, you will have found that the maximum and mini- mum directional derivatives are not equal to ||Vf(0,0)|| and –||Vf(0,0)||. This appears to contradict the Greatest Rate of Change Theorem given in Unit 7.2. What went wrong? Explain.
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