Proving Density in R: Subset of Rational Numbers P/2^n for n,p belong to Z

  • Thread starter HamedJafarian
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In summary, Hamed is asking for help proving that a set is dense in a given space. He is also asking for help with the δ, ε proof. He has been given the definition of a dense subset, but is unsure of how to go about proving it. He is also wondering if it is correct to use p,n when the p,n are close to each other in Z. Epsilon = 1/2m is chosen to be less than ε, and the proof is continued.
  • #1
HamedJafarian
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Homework Statement


How can I prove that the set of rational rational of the form P/2^n for n,p belong to Z is dense in R?


Homework Equations



How can I prove that a set is dense in R?

The Attempt at a Solution


I do not know how to check dense in R!
 
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  • #2
Welcome to PF!

HamedJafarian said:
How can I prove that the set of rational rational of the form P/2^n for n,p belong to Z is dense in R?

Hi Hamed! Welcome to PF! :smile:

With questions like this, always start with the definition

what definition has your professor given you for a dense subset?​
 
  • #3
HamedJafarian said:

Homework Statement


How can I prove that the set of rational rational of the form P/2^n for n,p belong to Z is dense in R?


Homework Equations



How can I prove that a set is dense in R?

The Attempt at a Solution


I do not know how to check dense in R!

You need to think about how R is defined.
 
  • #4


tiny-tim said:
Hi Hamed! Welcome to PF! :smile:

With questions like this, always start with the definition

what definition has your professor given you for a dense subset?​

Y is a subset of X,Y is dense in X, if for every x that belog to X, there is y blong to Y that is arbitary close to x.
 
  • #5
HamedJafarian said:
Y is a subset of X,Y is dense in X, if for every x that belog to X, there is y blong to Y that is arbitary close to x.

ok … then you need to prove that, for any number x in R, there is a number p/2n arbitrarily close to x.

Hint: choose epsilon = 1/2m :wink:
 
  • #6
tiny-tim said:
ok … then you need to prove that, for any number x in R, there is a number p/2n arbitrarily close to x.

Hint: choose epsilon = 1/2m :wink:

Is it correct for when the p ,n are blong to Z?
and with is it m?
 
  • #7
HamedJafarian said:
Is it correct for when the p ,n are blong to Z?
and with is it m?

sorry, Hamed, I've no idea what you mean. :redface:

anyway, I'm talking about the standard δ, ε proof … do you know what that is? :smile:
 
  • #8
Hi Hamed! Thanks for the PM. :smile:

(copy my "ε"! :wink:)
HamedJafarian said:
I mean that i must show that for every eps and x, there is a y that y-x<eps.how can i show this one?

Choose m so that 1/2m < ε,

and then … ? :smile:
 

What is a subset dense in R?

A subset dense in R is a subset of a topological space R that contains a dense subset of R. This means that the subset is spread out or evenly distributed throughout the entire space, without any gaps or holes.

What is the significance of having a subset dense in R?

Having a subset dense in R is important because it allows us to approximate any point in the space R with points from the subset. This is useful in many mathematical and scientific applications, such as in data analysis and function approximation.

How can I determine if a subset is dense in R?

To determine if a subset is dense in R, we can use the closure of the subset. If the closure of the subset is equal to the entire space R, then the subset is dense in R. Alternatively, we can also check if every point in R is either a limit point or a member of the subset.

What are some examples of subset dense in R?

Some examples of subset dense in R include the set of rational numbers in the real numbers, the set of algebraic numbers in the complex numbers, and the set of all continuous functions in the space of all functions.

Are there any practical applications of subset dense in R?

Yes, there are many practical applications of subset dense in R. For example, in data analysis, we can use a subset that is dense in R to approximate missing data points. In function approximation, we can use a subset that is dense in R to approximate any function in R. Additionally, subset dense in R is also used in various areas of engineering and physics, such as in signal processing and control theory.

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