Set Theory Proof(Using Identities)

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Discussion Overview

The discussion focuses on proving a set theory identity involving unions and intersections. Participants are exploring the proof of the equation A U B = (A ∩ B') U (A' ∩ B) U (A ∩ B) using set identities and axioms.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant requests help with a proof involving set identities after struggling for several hours.
  • Another participant suggests starting with the expression (A' ∩ B) U (A ∩ B) and asks what it simplifies to.
  • There is a discussion about the allowed axioms for the proof, including distributivity and DeMorgan's laws.
  • Participants confirm that (A' ∩ B) U (A ∩ B) simplifies to (A' U A) ∩ B.
  • One participant expresses confidence in their progress and mentions they will post their solution soon.
  • Another participant suggests that the reasoning could be shortened, implying that a more concise proof may exist.
  • There is a claim that A' U A equals the universal set, leading to further simplifications in the proof.
  • A final simplification is presented, showing the steps leading to A U B.

Areas of Agreement / Disagreement

Participants generally agree on the use of standard set axioms and the steps taken in the proof, but there is no consensus on the optimal length or method of the proof.

Contextual Notes

Some assumptions about the definitions of the sets and the context of the proof are not explicitly stated, which may affect the interpretation of the steps taken.

Who May Find This Useful

Students or individuals interested in set theory, particularly those looking for assistance with proofs involving set identities and operations.

ozymandris
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Hi, I've been trying for 3 hours to solve this proof using identities. I can't seem to get it.

Can i get a little help please?

Prove: A U B = (A ∩ B') U (A' ∩ B) U (A ∩ B)

thanks
 
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welcome to pf!

hi ozymandris! welcome to pf! :smile:

do the easy bit first …

what is (A' ∩ B) U (A ∩ B) ? :wink:
 
ozymandris said:
Hi, I've been trying for 3 hours to solve this proof using identities. I can't seem to get it.

Can i get a little help please?

Prove: A U B = (A ∩ B') U (A' ∩ B) U (A ∩ B)

thanks

Hey ozymandris and welcome to the forums.

What are you allowed to take for granted? Can you use normal set axioms like distributivity, DeMorgans laws, and so on?
 
chiro said:
Hey ozymandris and welcome to the forums.

What are you allowed to take for granted? Can you use normal set axioms like distributivity, DeMorgans laws, and so on?

(A' ∩ B) U (A ∩ B) = (A' U A) ∩ B


We're allowed all the normal set axioms, distributivity, deMorgan, etc etc
 
ozymandris said:
(A' ∩ B) U (A ∩ B) = (A' U A) ∩ B

yup! :smile:

and A' U A = … ? :wink:
 
tiny-tim said:
yup! :smile:

and A' U A = … ? :wink:

ok, i think I've gotten it. It took me nearly a page of workout. I'll post it when i have a minute to type it all in.
 
It should be only two lines, so you might want to see if you can shorten your reasoning.
 
tiny-tim said:
yup! :smile:

and A' U A = … ? :wink:

A' U A = \varnothing
 
(A ∩ B') U (A' U A) ∩ B

(A ∩ B') U {Universal} ∩ B

(A ∩ B') U B if i distribute from this

(A U B ) ∩ (B' U B)

A U B
 
  • #10
:biggrin: Woohoo! :biggrin:
 

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