Problem 9.1.19. The Topólógist's Sinė Function. Use the definition of continuity to show that Sæ sin (), if x +0 f(x) = if x = 0 %3D is continuous at 0.

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Chapter2: Second-order Linear Odes
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Analytical math

12:17 M
A personal.psu.edu/ecb!
+
To the naked eye, the graph of this
function looks like the lines y
= x. Of course, such a graph would not
be the graph of a function. Actually, both
0 and
of these lines have holes in them.
Wherever there is a point on one line
there is a "hole" on the other. Each of
these holes are the width of a single point
(that is, their "width" is zero!) so they are
invisible to the naked eye (or even
magnified under the most powerful
microscope available). This idea is
illustrated in the following graph
0.5-
-0.5
0.5
x irrationa)
x rational
Can such a function so "full of holes"
actually be continuous anywhere? It turns
out that we can use our definition to show
that this function is, in fact, continuous at
0 and at no other point.
II
II
Transcribed Image Text:12:17 M A personal.psu.edu/ecb! + To the naked eye, the graph of this function looks like the lines y = x. Of course, such a graph would not be the graph of a function. Actually, both 0 and of these lines have holes in them. Wherever there is a point on one line there is a "hole" on the other. Each of these holes are the width of a single point (that is, their "width" is zero!) so they are invisible to the naked eye (or even magnified under the most powerful microscope available). This idea is illustrated in the following graph 0.5- -0.5 0.5 x irrationa) x rational Can such a function so "full of holes" actually be continuous anywhere? It turns out that we can use our definition to show that this function is, in fact, continuous at 0 and at no other point. II II
12:17 i
Tact, continuous a U.
Problem 9.1.19. The Topologist's Sine
Function. Use the definition of
continuity to show that
x sin (-), ifx # 0
f(x) = {.
if x = 0
is continuous at 0.
Even more perplexing is the function
defined by
Sæ,
if x is rational
D(x) =
0,
10, if x is irrational .
To the naked eye, the graph of this
function looks like the lines y = 0 and
y = x. Of course, such a graph would not
be the graph of a function. Actually, both
of these lines have holes in them.
Wherever there is a point on one line
there is a "hole" on the other. Each of
these holes are the width of a single point
(that is, their "width" is zero!) so they are
invisible to the naked eye (or even
magnified under the most powerful
microscope available). This idea is
illustrated in the following graph
II
II
Transcribed Image Text:12:17 i Tact, continuous a U. Problem 9.1.19. The Topologist's Sine Function. Use the definition of continuity to show that x sin (-), ifx # 0 f(x) = {. if x = 0 is continuous at 0. Even more perplexing is the function defined by Sæ, if x is rational D(x) = 0, 10, if x is irrational . To the naked eye, the graph of this function looks like the lines y = 0 and y = x. Of course, such a graph would not be the graph of a function. Actually, both of these lines have holes in them. Wherever there is a point on one line there is a "hole" on the other. Each of these holes are the width of a single point (that is, their "width" is zero!) so they are invisible to the naked eye (or even magnified under the most powerful microscope available). This idea is illustrated in the following graph II II
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