tional derivative Daf. Describe precisely what the relationship is. b) In WA2 Q2(c) we saw that the existence of fa, fy and dsf is not sufficient to guarantee the differentiability of f. It might be tempting to think that differentiability will be guaranteed if all of the directional derivatives were to exist. This is not the case. In fact, this does not even guarantee continuity! Find an example of a function f : R² → R and a point (a, b) such that: (i) Daf(a, b) exists for every unit vector i E R², but (ii) f is not continuous at (a, b). Be sure to justify vour claims.

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter7: Analytic Trigonometry
Section7.6: The Inverse Trigonometric Functions
Problem 92E
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Question
Please solve only a part
(a) The simultaneous derivative df defined in WA2 Q2 is very closely related to the direc-
tional derivative Duf. Describe precisely what the relationship is.
(b) In WA2 Q2(c) we saw that the existence of fr, fy and dgf is not sufficient to guarantee
the differentiability of f. It might be tempting to think that differentiability will be
guaranteed if all of the directional derivatives were to exist. This is not the case. In
fact, this does not even guarantee continuity!
Find an example of a function f: R² → R and a point (a, b) such that:
(i) Dūf(a, b) exists for every unit vector i e R2, but
(ii) f is not continuous at (a, b).
Be sure to justify your claims.
(Tint: An ovomnlo of cuoh
f hoo onnoorod comouhoro in WA1
21
Transcribed Image Text:(a) The simultaneous derivative df defined in WA2 Q2 is very closely related to the direc- tional derivative Duf. Describe precisely what the relationship is. (b) In WA2 Q2(c) we saw that the existence of fr, fy and dgf is not sufficient to guarantee the differentiability of f. It might be tempting to think that differentiability will be guaranteed if all of the directional derivatives were to exist. This is not the case. In fact, this does not even guarantee continuity! Find an example of a function f: R² → R and a point (a, b) such that: (i) Dūf(a, b) exists for every unit vector i e R2, but (ii) f is not continuous at (a, b). Be sure to justify your claims. (Tint: An ovomnlo of cuoh f hoo onnoorod comouhoro in WA1 21
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