Alternative proof for the 1st mean-value theorem for integrals

In summary, the 1st mean-value theorem for integrals can be proven by applying the Lagrange mean-value theorem to an integral with a variable upper limit. This can also be done using the Cauchy mean value theorem, utilizing the functions F(t) = \int_{a}^{t}f(x)g(x)\;dx and G(t) = \int_{a}^{t}g(x)\;dx and the existence of \xi such that \frac{F'(\xi)}{G'(\xi)} = \frac{F(b)-F(a)}{G(b)-G(a)}.
  • #1
y_lindsay
17
0
can anyone tell me how to prove the 1st mean-value theorem for integral
[tex]\int^{b}_{a}f(x)g(x)dx=f(\xi)\int^{b}_{a}g(x)dx[/tex]
by applying Lagrange mean-value theorem to an integral with variable upper limit?
thanks a lot.
 
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  • #2
I think I've seen a proof that uses the Cauchy Mean Value Theorem using

[tex]F(t) = \int_{a}^{t}f(x)g(x)\;dx[/tex]

[tex]G(t) = \int_{a}^{t}g(x)\;dx[/tex]

So there exists [itex]\xi[/itex] so that

[tex]\frac{F'(\xi)}{G'(\xi)} = \frac{F(b)-F(a)}{G(b)-G(a)}[/tex]

or at least that is what I remember.

--Elucidus
 

Related to Alternative proof for the 1st mean-value theorem for integrals

1. What is the 1st mean-value theorem for integrals?

The 1st mean-value theorem for integrals states that if a function f(x) is continuous on the closed interval [a,b] and differentiable on the open interval (a,b), then there exists a value c in (a,b) such that the definite integral of f(x) from a to b is equal to f(c) multiplied by the length of the interval (b-a).

2. What is the traditional proof for the 1st mean-value theorem for integrals?

The traditional proof for the 1st mean-value theorem for integrals involves using the intermediate value theorem for derivatives and the fundamental theorem of calculus.

3. How is the alternative proof for the 1st mean-value theorem for integrals different?

The alternative proof for the 1st mean-value theorem for integrals uses the concept of the mean-value theorem for derivatives and the Cauchy mean-value theorem.

4. What are the advantages of using the alternative proof for the 1st mean-value theorem for integrals?

The alternative proof is often considered more intuitive and easier to understand compared to the traditional proof. It also provides a deeper understanding of the concept of mean-value and its application in calculus.

5. Can the alternative proof be applied to other mean-value theorems?

Yes, the alternative proof for the 1st mean-value theorem for integrals can be extended to other mean-value theorems, such as the 2nd mean-value theorem for integrals and the mean-value theorem for higher-order derivatives.

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