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Prove a+b=b+a for integers

  • Thread starter iwonde
  • Start date
  • #1
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Homework Statement


Prove that for any two integers a and b, a+b=b+a. You may use the face that this holds for natural numbers.


Homework Equations





The Attempt at a Solution


a=(x,y), b=(u,v)
x,y,u,v are natural numbers
a+b = (x,y)+(u,v) = (u,v)+ (x,y) = b+a

I'm not sure if my attempt was correct.
 

Answers and Replies

  • #2
392
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(x,y)+(u,v) = (u,v)+ (x,y)
This step assumes the conclusion. You have to prove it.

Hint: What is the definition of (x,y)+(u,v)?
 
  • #3
33,179
4,859

Homework Statement


Prove that for any two integers a and b, a+b=b+a. You may use the face that this holds for natural numbers.


Homework Equations





The Attempt at a Solution


a=(x,y), b=(u,v)
What do the equations above mean? a and b are integers, not ordered pairs.
x,y,u,v are natural numbers
a+b = (x,y)+(u,v) = (u,v)+ (x,y) = b+a

I'm not sure if my attempt was correct.
 
  • #4
Hurkyl
Staff Emeritus
Science Advisor
Gold Member
14,916
17
What do the equations above mean? a and b are integers, not ordered pairs.
I suspect the opening poster forgot to tell us that he's working with a specific presentation of the integers -- represented as the set of ordered pairs of natural numbers modulo an equivalence relation -- along with the definition of + that he's using.

(Of course, maybe that's exactly what you were prompting the opening poster to say -- if so, sorry 'bout that)
 
  • #5
33,179
4,859
Nope, I wasn't thinking that at all, so no problem.
 

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