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I am reading Manfred Stoll's book: Introduction to Real Analysis.
I need help with Stoll's proof of The Fundamental Theorem of the Calculus - Stoll: Theorem 6.3.2
Stoll's statement of Theorem 6.3.2 and its proof reads as follows:View attachment 3952
View attachment 3953
In the above proof we read:
Since
\(\displaystyle \mathscr{L}( \mathscr{P} , f ) \le \sum_{i = 1}^n f(t_i) \Delta x_i \le \mathscr{U}( \mathscr{P} , f )\)
we have
\(\displaystyle \underline{\int^b_a}f(x) dx \le F(b) - F(a) \le \overline{\int^b_a} f(x) dx \)My question is as follows: How do we know this is true? or Why exactly is this the case?
Can someone explain?
To restate my question:Since \(\displaystyle \underline{\int^b_a} f(x) dx\) is the supremum of \(\displaystyle \mathscr{L}( \mathscr{P} , f )\) over all partitions \(\displaystyle \mathscr{P}\) how do we know that it is less than F(b) - F(a)? ... ...... ... that is, is it possible for the quantity \(\displaystyle \mathscr{L}( \mathscr{P} , f ) \)to be less than \(\displaystyle F(b) - F(a)\) for all partitions \(\displaystyle \mathscr{P}\) but for the supremum over all partitions to fail to be less than \(\displaystyle F(b) - F(a)\)? ... ...
Hmm ... ... reflecting ... ... beginning to think this is not possible ... but how would you frame a rigorous symbolic argument of this?
Can someone please help?
Peter
I need help with Stoll's proof of The Fundamental Theorem of the Calculus - Stoll: Theorem 6.3.2
Stoll's statement of Theorem 6.3.2 and its proof reads as follows:View attachment 3952
View attachment 3953
In the above proof we read:
Since
\(\displaystyle \mathscr{L}( \mathscr{P} , f ) \le \sum_{i = 1}^n f(t_i) \Delta x_i \le \mathscr{U}( \mathscr{P} , f )\)
we have
\(\displaystyle \underline{\int^b_a}f(x) dx \le F(b) - F(a) \le \overline{\int^b_a} f(x) dx \)My question is as follows: How do we know this is true? or Why exactly is this the case?
Can someone explain?
To restate my question:Since \(\displaystyle \underline{\int^b_a} f(x) dx\) is the supremum of \(\displaystyle \mathscr{L}( \mathscr{P} , f )\) over all partitions \(\displaystyle \mathscr{P}\) how do we know that it is less than F(b) - F(a)? ... ...... ... that is, is it possible for the quantity \(\displaystyle \mathscr{L}( \mathscr{P} , f ) \)to be less than \(\displaystyle F(b) - F(a)\) for all partitions \(\displaystyle \mathscr{P}\) but for the supremum over all partitions to fail to be less than \(\displaystyle F(b) - F(a)\)? ... ...
Hmm ... ... reflecting ... ... beginning to think this is not possible ... but how would you frame a rigorous symbolic argument of this?
Can someone please help?
Peter