Riemann Integrability, Linear Transformations

In summary, the conversation discusses the proof for the statement that if f and g are Riemann integrable on [a,b], then for c and d real numbers, I(cf + dg) = cI(f) + dI(g). The conversation also mentions the proofs for the propositions I(cf) = I(f) and I(f+g) = I(f) + I(g), and how they can be used to prove the statement. It is suggested that proving that if f is Riemann integrable then so is cf would complete the proof.
  • #1
missavvy
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0

Homework Statement



If f,g are Riemann integrable on [a,b], then for c,d real numbers,

(let I denote the integral from a to b)

I (cf + dg) = c I (f) + d I (g)


Homework Equations





The Attempt at a Solution



I have the proofs for

c I(f) = I (cf)

and

I (f+g) = I (f) + I(g)

I'm wondering how would I put them together to prove the statement?
Can I just say that because I know these 2 propositions are true, then any linear combination would also work?
 
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  • #2
Should be easy to put them together.

I(cf + cg) = I(cf) + I(dg) (since you know I(f+g) = I(f) + I(g), just replace f with cf and g with dg)
= cI(f) + dI(g) (since you know I(cf) = I(f))

I think the only problem with this is that you have to prove that if f is Riemann integrable then so is cf, which shouldn't be hard.
 

1. What is Riemann Integrability?

Riemann Integrability is a mathematical concept used to determine whether a function is integrable or not. It was developed by German mathematician Bernhard Riemann and is based on the idea that a function is integrable if the area under its curve can be approximated by a finite number of rectangles.

2. How is Riemann Integrability different from other types of integrability?

Riemann Integrability is a specific type of integrability that is based on the Riemann sum, which divides the area under a curve into smaller rectangles. Other types of integrability, such as Lebesgue Integrability, use different methods to approximate the area under a curve.

3. What is a linear transformation?

A linear transformation is a function that maps one vector space to another in a way that preserves the operations of addition and scalar multiplication. This means that the output of a linear transformation can be obtained by adding and scaling the inputs in a certain way.

4. How do linear transformations relate to Riemann Integrability?

Linear transformations play a crucial role in Riemann Integrability because they can be used to transform a function into a simpler form, making it easier to determine its integrability. By applying a linear transformation to a function, the area under its curve can be redefined in a way that is easier to approximate using rectangles.

5. Can any function be made Riemann Integrable?

No, not all functions are Riemann Integrable. A function must meet certain criteria, such as being continuous on a closed interval, in order to be considered Riemann Integrable. Additionally, some functions may be integrable using other methods, such as Lebesgue Integrability, even if they are not considered Riemann Integrable.

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