This exercise provides an example of a function f: R² → R such that all first partial derivatives exist everywhere, but ƒ is discontinuous. Let f(x, y) = { 2xy² x²+y4 if (x, y) = (0,0) (0,0) if (x, y) = (0,0). (a) Calculate (D₁f)(x,y) and (D₂f)(x, y) at all points (x,y) different from (0,0). (b) Calculate (D₁ƒ)(0,0) and (D₂f)(0,0) directly from the definition of derivative. (c) Show that f is discontinuous at (0,0) by showing limy→o ƒ(y², y) ‡ 0.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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This exercise provides an example of a function f: R² → R such that all
first partial derivatives exist everywhere, but ƒ is discontinuous. Let
f(x,y) = {
2xy²
x²+y4
if (x, y) = (0,0)
(0,0) if (x, y) = (0,0).
(a) Calculate (D₁f)(x,y) and (D₂f)(x, y) at all points (x,y) different
from (0,0).
(b) Calculate (D₁ƒ)(0,0) and (D₂f)(0,0) directly from the definition of
derivative.
(c) Show that f is discontinuous at (0,0) by showing limy→o ƒ(y², y) ‡ 0.
Transcribed Image Text:This exercise provides an example of a function f: R² → R such that all first partial derivatives exist everywhere, but ƒ is discontinuous. Let f(x,y) = { 2xy² x²+y4 if (x, y) = (0,0) (0,0) if (x, y) = (0,0). (a) Calculate (D₁f)(x,y) and (D₂f)(x, y) at all points (x,y) different from (0,0). (b) Calculate (D₁ƒ)(0,0) and (D₂f)(0,0) directly from the definition of derivative. (c) Show that f is discontinuous at (0,0) by showing limy→o ƒ(y², y) ‡ 0.
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