# Quick question about two sets...

1. Dec 6, 2017

1. The problem statement, all variables and given/known data
Is the set (r,-r,0) the same as the set (-r,r,0)

Sorry I need to know the answer to this right now, somebody in class confused me and I can't talk to my teacher right now.

My answer: yes it is the same set. Can anyone just give me a quick yes/no?

2. Relevant equations

3. The attempt at a solution

2. Dec 6, 2017

### BvU

I have to brake for a car in front of me, so I can't answer 'it depends' right now !

good luck with your test !

3. Dec 6, 2017

### Staff: Mentor

Yes, as sets they are the same. Order doesn't matter here.

4. Dec 6, 2017

### BvU

I wasn't really in a car, but safely behind my desktop. Just didn't want to interfere in a testing situation

If the order of elements in a set matters, we call it a sequence. (You need a sequence of instructions when asking directions; with a set you wouldn't know what to do first)

A set is a collection. Two collections are the same if they contain the same elements. Yours do

5. Dec 6, 2017

### Ray Vickson

Your notation is poor: in Mathematics, we almost always denote sets using curly brackets, like this: $\{ r, -r,0 \}$, and in that case, order does not matter: $\{ r,-r,0 \} = \{ r,-r,0 \} = \{ r,0,-r \} = \{ -r,0,r \} = \{ 0,r,-r \} = \{ 0,-r,r \}.$ Other types of brackets like ( , ) , [ , ] or < , > denote objects like lists, vectors, arrays, sequences, etc., and for all of them order is crucial.