F is integrable but has no indefinite integral Let f ( x ) = { <mtabl

Michelle Mendoza

Michelle Mendoza

Answered question

2022-07-03

F is integrable but has no indefinite integral
Let f ( x ) = { 0 ,   x 0 1 , x = 0.
Then f is clearly integrable, yet has no antiderivative, on any interval containing 0, since any such antiderivative would have a constant value on each side of 0 and have slope 1 at 0 an impossibility.
So does this mean that f has no indefinite integral?
EDIT
My understanding is that the indefinite integral of f is the family of all the antiderivatives of f, and conceptually requires some antiderivative to be defined on the entire domain. Is this correct?

Answer & Explanation

Sanaa Hinton

Sanaa Hinton

Beginner2022-07-04Added 15 answers

Step 1
Attempting to express f's indefinite integral on its entire domain R runs into a technical problem at x = 0 ::
f ( x ) d x = { C 1 ,   x < 0 ? ? ? , x = 0 C 2 ,   x > 0 .
Step 2
No indefinite integral no antiderivative.
On the other hand, f has an indefinite integral (and antiderivative) on every interval not containing 0.
Frank Day

Frank Day

Beginner2022-07-05Added 4 answers

Step 1
This is a matter of definitions. Usually an antiderivative of a function f is any function whose derivative is f. The indefinite integral usually denotes the set of all antiderivatives.
Since every derivative satisfies the intermediate values property, your function f cannot be a derivative and hence has no indefinite integral.
Step 2
A different thing is the integral function which might be defined as a function F such that
a b f ( x ) d x = F ( b ) F ( a ) .
This exists for all integrable functions.
The fundamental theorem of Calculus states that the two concepts agree for continuous functions.

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