7x2 – 2y2 EXAMPLE 1 Show that lim does not exist. (x, y)-(0, 0) x² + y2 SOLUTION Let f(x, y) = (7x² – 2y²)/(x² + y²). First, let's approach (0, 0) along the x-axis. Then y = gives f(x, 0) = 7x2/x² = for all x + 0, so f(x, у) > as (x, y) → (0, 0) along the x-axis. We now approach along the y-axis by putting x = . Then f(0, y) = -2y2/y2 = for all y + 0, so f(x, у) > as (x, y) → (0, 0) along the y-axis. Since f has two different limits along two different lines, the given limit does not exist.

Calculus: Early Transcendentals
8th Edition
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Author:James Stewart
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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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7x2 – 2y2
ΕΧΑMPLE 1
Show that
lim
does not exist.
(х, у) — (0, 0) х2 + у2
SOLUTION
Let f(x, y) = (7x² – 2y2)/(x2 + y2). First, let's approach (0, 0) along the x-axis. Then y =
gives
f(x, 0) = 7x²/x² =
for all x + 0, so
f(x, у) —
as (x, y) → (0, 0) along the x-axis.
We now approach along the y-axis by putting x =
. Then f(0, y) = -2y2/y2 =
for all y + 0, so
f(x, у) —
as (x, y) → (0, 0) along the y-axis.
Since f has two different limits along two different lines, the given limit does not exist.
Transcribed Image Text:7x2 – 2y2 ΕΧΑMPLE 1 Show that lim does not exist. (х, у) — (0, 0) х2 + у2 SOLUTION Let f(x, y) = (7x² – 2y2)/(x2 + y2). First, let's approach (0, 0) along the x-axis. Then y = gives f(x, 0) = 7x²/x² = for all x + 0, so f(x, у) — as (x, y) → (0, 0) along the x-axis. We now approach along the y-axis by putting x = . Then f(0, y) = -2y2/y2 = for all y + 0, so f(x, у) — as (x, y) → (0, 0) along the y-axis. Since f has two different limits along two different lines, the given limit does not exist.
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