Let f(x, y) = xy + x − y be defined on the closed disk {(x, y) ∈ R2 : x2 + y2 ≤ 4} of radius 2. (a) Find the maximum and minimum of Duf at (0, 0) over all unit vectors u. (b) Find the maximum and minimum of Duf over all points in the disk {(x, y) ∈ R2 : x2 + y2 ≤ 4} and all unit vectors u. (Hint: Think of |∇f|2 as a function of x and y in the disk.)

Elementary Linear Algebra (MindTap Course List)
8th Edition
ISBN:9781305658004
Author:Ron Larson
Publisher:Ron Larson
Chapter4: Vector Spaces
Section4.3: Subspaces Of Vector Spaces
Problem 49E
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Let f(x, y) = xy + x − y be defined on the closed disk {(x, y) ∈ R2 : x2 + y2 ≤ 4} of radius 2.

(a) Find the maximum and minimum of Duf at (0, 0) over all unit vectors u.

(b) Find the maximum and minimum of Duf over all points in the disk {(x, y) ∈ R2 : x2 + y2 ≤ 4} and all unit vectors u. (Hint: Think of |∇f|2 as a function of x and y in the disk.)

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