Solving Discrete Math Question: Proving ∪n=2∞[0,1 - 1/n] = [0,1)

In summary: If x is any number between 0 and 1, x is in one of those intervals. If x= 1, it is in none of them. So the union is all numbers between 0 and 1 except 1.In summary, the conversation is discussing how to prove that the union of intervals from n=2 to infinity, [0, 1-1/n], is equal to [0, 1) and how to explain why the union does not contain 1 but does contain all other numbers between 0 and 1. The solution involves showing that for any positive number x, there is an n such that 1-1/n is less than x, thus making the union include
  • #1
bensoa1
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Poster received a warning about not including an attempt

Homework Statement


Show that,
n=2[0,1 - 1/n] = [0,1)

Homework Equations

The Attempt at a Solution

 
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  • #2
bensoa1 said:

Homework Statement


Show that,
n=2[0,1 - 1/n] = [0,1)

Homework Equations

The Attempt at a Solution


Well, explain why the union of all of those intervals contains everything in [0,1] except for 1.
 
  • #3
Dick said:
Well, explain why the union of all of those intervals contains everything in [0,1] except for 1.
This was the plan of action I wanted to take, however, I'm not sure of the appropriate way to do that
 
  • #4
bensoa1 said:
This was the plan of action I wanted to take, however, I'm not sure of the appropriate way to do that

Start by explaining why it doesn't contain 1. Then continue by explaining why it does contain 99/100. Then extrapolate from there. Think about it.
 
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  • #5
Dick said:
Start by explaining why it doesn't contain 1. Then continue by explaining why it does contain 99/100. Then extrapolate from there. Think about it.
My method was to first show that when n = 2 the answer was [0,1). Then I had an arbitrary integer greater than 0, such that ∪n=2[0,1-1/(k+2)) = [0,1). Would this be sufficient?
 
  • #6
bensoa1 said:
My method was to first show that when n = 2 the answer was [0,1). Then I had an arbitrary integer greater than 0, such that ∪n=2[0,1-1/(k+2)) = [0,1). Would this be sufficient?

n goes from 2 to infinity in the union. You can't pick it to be 2. Start by explaining why 1 is not in the union.
 
  • #7
Dick said:
n goes from 2 to infinity in the union. You can't pick it to be 2. Start by explaining why 1 is not in the union.
What is the mathematical proof to use in order to show that it isn't?
 
  • #8
Dick said:
n goes from 2 to infinity in the union. You can't pick it to be 2. Start by explaining why 1 is not in the union.
Okay so I did this, ∪n=2∞[0,1 - 1/n] = [0,1/2), [0,2/3), [0,3/4),...,[0,n-1/n). Since n-1/n < 1, by union properties ∪n=2∞[0,1 - 1/n] = [0,1). Would this suffice?
 
  • #9
The union is [0,1/2]U[0,2/3]U[0,3/4]U[0,4/5]... Don't you see why 1 isn't in it and any number 0<=x<1 is? Just explain in words.
 
  • #10
bensoa1 said:
My method was to first show that when n = 2 the answer was [0,1). Then I had an arbitrary integer greater than 0, such that ∪n=2[0,1-1/(k+2)) = [0,1). Would this be sufficient?
What do you mean "when n= 2 the answer was [0, 1)"? When n= 2. [0, 1- 1/n]= [0, 1- 1/2]= [0, 1/2]. That is NOT "[0, 1)"!

You need to focus on 1- 1/n. Do you see that there is NO n such that [itex]1\le 1- 1/n[/itex]? Why not?

On the other hand, if x is any positive number there exist n such that 1/n< x. Why? Then what can you say about 1- 1/n?

Do you understand that the right hand side is
[tex][0, 1/2]\cup[0, 2/3]\cup[0, 3/4]\cup[0, 4/5]\cdot\cdot\cdot[/tex]?
 
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FAQ: Solving Discrete Math Question: Proving ∪n=2∞[0,1 - 1/n] = [0,1)

What is Discrete Math?

Discrete Math is a branch of mathematics that deals with countable and finite quantities, as opposed to continuous quantities like real numbers. It is used to study and solve problems in computer science, algorithms, and cryptography.

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