# Thread: From Riemanns sum to definite integral

1. ## From Riemanns sum to definite integral

Dear All!
I found this as an explanation!

Definite Integral Proof? - Yahoo! Answers

The problem is that I just dont understand it still form the first line:
F(X1) – F(a) = F’(C1) * (X1-a) = F’(C1)*ΔX1 = f(C1)* ΔX1

Please, how do we get this?
Many thanks!!!

2. ## Re: From Riemanns sum to definite integral

Originally Posted by Boo
Dear All!
I found this as an explanation!
Definite Integral Proof? - Yahoo! Answers
The problem is that I just dont understand it still form the first line:
F(X1) – F(a) = F’(C1) * (X1-a) = F’(C1)*ΔX1 = f(C1)* ΔX1
Please, how do we get this?
Many thanks!!!
I do not think that anyone will be angry, certainly not me, at your question.
However, I will tell that I have given a semester long course on the theory of the integral in an attempt to completely answer your question.

3. ## Re: From Riemanns sum to definite integral

Can someone give me the hint?
Everyone I know avoids to answer....
What is $C_1$???

4. ## Re: From Riemanns sum to definite integral

Originally Posted by Boo
Dear All!
I found this as an explanation!

Definite Integral Proof? - Yahoo! Answers

The problem is that I just dont understand it still form the first line:
F(X1) – F(a) = F’(C1) * (X1-a) = F’(C1)*ΔX1 = f(C1)* ΔX1
C1 is a point chosen so that F(X1) – F(a) = F’(C1) * (X1-a). The fact that there exist such a value, C1, follows from the "mean value theorem". The fact that those equal F'(C1)*ΔX1 is just that ΔX1 is defined as (X1- a). And the fact that F'(C1)ΔX1= f(C1) follows from the fact "f" is defined as F'.

Please, how do we get this?
Many thanks!!!