• Support PF! Buy your school textbooks, materials and every day products Here!

Equivalence Relation

  • Thread starter nikie1o2
  • Start date
  • #1
7
0

Homework Statement



Consider the set A={(u,v,w) in R^3 : u^2+v^2>0} and define a relation ~ on A by (u,v,w)~(u',v',w') IFF there exists a "k" in R, where k doesnt equal 0: (u',v',w')=(ku,kv,kw)

Prove that ~ is an equivalence relation of A


Homework Equations


I honestly dont know where to start, i know i need to satisfy the reflexive, symmetric & transitive requirements but i dont even know what the relation is here. Any help is very much appreciated.


The Attempt at a Solution

 

Answers and Replies

  • #2
vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
14,553
1,158
You're given the relation. Two vectors (u,v,w) and (u',v',w') are related if they are non-zero multiples of each other. For example, (1,1,1) ~ (2,2,2) since (2,2,2)=(2x1, 2x1, 2x1), i.e. k=2.

Homework Statement



Consider the set A={(u,v,w) in R^3 : u^2+v^2>0} and define a relation ~ on A by (u,v,w)~(u',v',w') IFF there exists a "k" in R, where k doesnt equal 0: (u',v',w')=(ku,kv,kw)

Prove that ~ is an equivalence relation of A


Homework Equations


I honestly dont know where to start, i know i need to satisfy the reflexive, symmetric & transitive requirements but i dont even know what the relation is here. Any help is very much appreciated.


The Attempt at a Solution

 
  • #3
7
0
You're given the relation. Two vectors (u,v,w) and (u',v',w') are related if they are non-zero multiples of each other. For example, (1,1,1) ~ (2,2,2) since (2,2,2)=(2x1, 2x1, 2x1), i.e. k=2.
Ok, So to show its reflexive i can pick an real numbers? I can say (u,v,w)=(1,1,1) so (1,1,1) R (1,1,1) ???
 
  • #4
41
0
No, for reflexive, you'd need to look at a general triple (u,v,w). What does it mean to have
(u,v,w) ~ (u,v,w) ?

Write it out and find a value for k.

You'll need to work with general triples for all of the axioms for an equivalence relation.
(if you really get stuck, you might work with specific points to get a handle on what's happening, but you can't choose specific points for the proof)
 
  • #5
vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
14,553
1,158
Ok, So to show its reflexive i can pick an real numbers? I can say (u,v,w)=(1,1,1) so (1,1,1) R (1,1,1) ???
No, I was just using specific numbers as an example. As Mathnerdmo said, for a proof, you need to show it's true for the general case.
 

Related Threads for: Equivalence Relation

  • Last Post
Replies
13
Views
1K
  • Last Post
Replies
5
Views
990
  • Last Post
Replies
9
Views
2K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
3
Views
2K
Top