Show f e Lla, b] if and only if |f| E L[a,b].

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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 Show f ∈ L∞[a, b] if and only if |f| ∈ L∞[a, b].

(10) Show fe L°la, b] if and only if |f] e L[a,b).
Transcribed Image Text:(10) Show fe L°la, b] if and only if |f] e L[a,b).
Expert Solution
Step 1

The infinity norm of a function f on a,b is defined as:

f=infk:fxk, almost every where on a,b.

Suppose fLa,b, therefore there exists k0 such that:

                f=k

Now consider the function f, defined as:

   fx=fx, xa,b

Therefore, infinity norm of f can be calculated as:

f=infM:fxM, almost every where on a,b=infM:fxM, almost every where on a,b=f=k

Hence, fLa,b.

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