Real Analysis proof continuity

In summary, to show that the function f(x)=x is continuous at every point p, we can choose any arbitrary positive value for epsilon (ε) and set delta (δ) equal to epsilon. Then, for every x in the real numbers, if the absolute value of the difference between x and p is less than delta, then the absolute value of the difference between f(x) and f(p) is also less than epsilon. In other words, the function f(x)=x is continuous at every point p.
  • #1
kbrono
16
0
Show that the function f(x)=x is continuous at every point p.

Here's what I think but not sure if i can make one assumption.

Let [tex]\epsilon[/tex]>0 and let [tex]\delta[/tex]=[tex]\epsilon[/tex] such that for every x[tex]\in[/tex][tex]\Re[/tex] |x-p|<[tex]\delta[/tex]=[tex]\epsilon[/tex]. Now x=f(x) and p=f(p) so we have |f(x)-f(p)|<[tex]\epsilon[/tex].




Or...

can i just say that |x-p| [tex]\leq[/tex] |f(x)-f(p)|<[tex]\epsilon[/tex]. ?


Thanks
 
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  • #2
kbrono said:
Let [tex]\epsilon[/tex]>0 and let [tex]\delta[/tex]=[tex]\epsilon[/tex] such that for every x[tex]\in[/tex][tex]\Re[/tex] |x-p|<[tex]\delta[/tex]=[tex]\epsilon[/tex]. Now x=f(x) and p=f(p) so we have |f(x)-f(p)|<[tex]\epsilon[/tex].

This is correct!
I didn't really understand what your point was in your other idea...
 
  • #3
and you can say
[tex] |f(x)-f(p)| = |x-p| < \delta = \epsilon [/tex]
 

Related to Real Analysis proof continuity

1. What is the definition of continuity in real analysis?

The formal definition of continuity in real analysis is that a function f is continuous at a point c if the limit of f(x) as x approaches c is equal to f(c). In other words, the limit of the function must exist and be equal to the value of the function at that point.

2. How is continuity of a function proven using the epsilon-delta definition?

The epsilon-delta definition of continuity states that for any epsilon greater than 0, there exists a delta greater than 0 such that for all x within delta of c, the difference between f(x) and f(c) is less than epsilon. To prove continuity using this definition, one must show that for any given epsilon, a suitable delta can be found that satisfies this condition.

3. What is the role of limits in proving continuity?

Limits are crucial in proving continuity because they provide a way to evaluate the behavior of a function near a given point. In order for a function to be continuous at a point c, the limit of the function as x approaches c must exist and be equal to f(c). This ensures that the function is well-behaved and does not have any discontinuities at that point.

4. Can a function be continuous at some points and not at others?

Yes, a function can be continuous at some points and not at others. In fact, there are three types of discontinuities that a function can have: removable, jump, and essential. A removable discontinuity occurs when a function is not defined at a point, but can be made continuous by defining the function at that point. A jump discontinuity occurs when the left and right limits of a function at a point are finite, but not equal. An essential discontinuity occurs when the left and right limits of a function at a point are infinite.

5. What are some common techniques used in real analysis proofs for continuity?

Some common techniques used in real analysis proofs for continuity include the epsilon-delta definition, the squeeze theorem, and the intermediate value theorem. The limit laws and continuity laws are also frequently used to simplify proofs. Additionally, understanding the properties of continuous functions and how they behave near different types of discontinuities can be helpful in constructing proofs for continuity.

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