Problem 4: Define f: [0, 1] R by f(x) = 2x if x is irrational and f(x) =-1 if x is rational. Carefully demonstrate, using Definition 7.1.3, that f is not Riemann-integrable on [0,1]. ww.

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Problem 4: Define f: [0, 1] → R by f(x) = 2x if x is irrational and f(x) = -1 if x is
rational. Carefully demonstrate, using Definition 7.1.3, that f is not Riemann-integrable on
[0, 1].
%3D
Solution:
7.1.3 DEFINITION
Let f be a bounded function defined on [a, b]. Then
U(f) = inf {U(fS, P): P is a partition of [a, b]}
is called the upper integral of f on [a, b]. Similarly,
L(f) = sup {L(f. P): P is a partition of [a, b]}
%3D
is called the lower integral of f on [a, b). If these upper and lower integrals
are equal, then we say that f is Riemann integrable on [a, b], and we denote
their common value by f or by LSx) dx. That is, if L(f)= U(f), then
S-Lrmdx = LUS) = U(S)
is the Riemann integral of f on [a, b].
Transcribed Image Text:Problem 4: Define f: [0, 1] → R by f(x) = 2x if x is irrational and f(x) = -1 if x is rational. Carefully demonstrate, using Definition 7.1.3, that f is not Riemann-integrable on [0, 1]. %3D Solution: 7.1.3 DEFINITION Let f be a bounded function defined on [a, b]. Then U(f) = inf {U(fS, P): P is a partition of [a, b]} is called the upper integral of f on [a, b]. Similarly, L(f) = sup {L(f. P): P is a partition of [a, b]} %3D is called the lower integral of f on [a, b). If these upper and lower integrals are equal, then we say that f is Riemann integrable on [a, b], and we denote their common value by f or by LSx) dx. That is, if L(f)= U(f), then S-Lrmdx = LUS) = U(S) is the Riemann integral of f on [a, b].
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