# Thread: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

1. ## help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

i need to figure out relations, and to that we were taught to find ordered pairs and then put them in a matrix, and then i can determine if this equation is reflexive, stymeteric,antisymmertic and so.

i don;t know how to figure out what the ordered pairs are though.

2. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

i need to figure out relations, and to that we were taught to find ordered pairs and then put them in a matrix, and then i can determine if this equation is reflexive, symmetric, asymmetric and so.
First, you must know on what set the relation is defined. You failed to do that.

Second, I have no idea what put them in a matrix could mean. So please tell us.

Third, do you know what reflexive, symmetric, asymmetric mean?

Now I will give you three pairs in the relation on $\mathbb{N}$
$(2,2),~(4,7),~\&~(7,4)$

3. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

i don;t know how to figure out what the ordered pairs are though.
You could start by reading the introduction of the Wikipedia article about ordered pairs and then writing, say, 6 ordered pairs (x, y) of integers such that 3 divides x - y. Note that it is my guess that elements of pairs are integers. The problem that you are trying to solve is supposed to specify the set on which the relation is considered.

i need to figure out relations, and to that we were taught to find ordered pairs and then put them in a matrix
You can write the matrix corresponding to a relation if the relation is on a finite set. If this relation is indeed considered on the set of all integers, then the matrix would be infinite.

4. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

Originally Posted by Plato
First, you must know on what set the relation is defined. You failed to do that.

Second, I have no idea what put them in a matrix could mean. So please tell us.

Third, do you know what reflexive, symmetric, asymmetric mean?

Now I will give you three pairs in the relation on $\mathbb{N}$
$(2,2),~(4,7),~\&~(7,4)$
sorry about that, yes i know what reflexive, symmetric, asymmetric mean

the question is "determine whether each relation defined on the set of positive intergers is reflexivem symmetric,antisymmertic,transitive, and or partial order.

then it gives 5 problems but the first and the one i'm trying to figure out is. x,y)∈r if 3 divides x-y

(x,y)∈r if 3 divides x-y to do this we need to figure out the elements of R so we can get our ordered pair. Those elements are (1,1),(1,2)(1,3)(2,1)(2,2)(2,3)(3,1)(3,2)(3,3)(4,4 ) with this ordered pair we can fill in our matrix. From the matrix we can see that this is an equivalence relation.
x x x x x
y 1 2 3 4
Y 1 x x x o
Y 2 x x x o
Y 3 x x x o
y 4 o o o x

after fumbling around the above is what i came up with but not sure if it's right. and i don;t know how to get the elements of R. i found those in the back of the book in the answer section for a previous question.

5. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

ok so that is totally wrong, to find my set i need to have 2 number's and that's any 2 numbers that when subtracted and then divied by 3 has no remander, so the set i came up with is (13,1)(14,2)(15,3)(16,4)(17,5) 13-1 = 12 / 3 = 4. now i have to determine if this set is reflexive symmetric,antisymmertic,transitive, and or partial order.

does anyone know and if you do can you explain how you figured it out.

6. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

Every integer has remainder, when divided by 3, of 0, 1, or 2. It should be easy to see that two numbers, x and y, have x- y divisible by 3 if and only if they have the same remainder when divided by 3. One equivalence class is {0, 3, -3, 6, -6, ...}, the multiples of 3. Another is {1, -2, 4, -5, 7, -8, ...}, numbers that have remainder 1 when divided by 3. The last equivalence class is {2, -1, 5, -4, 8, -7, 11, -10, ...}, numbers that have remainder 2 when divided by 3.

The ordered pairs are any pairs of numbers from one of those three sets.

7. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

Originally Posted by HallsofIvy
Every integer has remainder, when divided by 3, of 0, 1, or 2. It should be easy to see that two numbers, x and y, have x- y divisible by 3 if and only if they have the same remainder when divided by 3. One equivalence class is {0, 3, -3, 6, -6, ...}, the multiples of 3. Another is {1, -2, 4, -5, 7, -8, ...}, numbers that have remainder 1 when divided by 3. The last equivalence class is {2, -1, 5, -4, 8, -7, 11, -10, ...}, numbers that have remainder 2 when divided by 3.

The ordered pairs are any pairs of numbers from one of those three sets.
well according to my discreate math professor the set i put up was correct, and the problem says "determine whether each relation defined on the set of positive intergers"
there can't be negatives in the set so i don;t think those sets are correct.

8. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

determine whether each relation defined on the set of positive intergers is reflexivem symmetric,antisymmertic,transitive, and or partial order.

(x,y)∈r if 3 divides x-y

To do this we need to figure out the elements of R so we can get our ordered pair. Those elements are (13,1)(14,2)(15,3)(16,4)(17,5) with this ordered pair we can fill in our matrix. From the matrix we can see that this is a refelxive relation.
y y y y y y
X 1 2 3 4 5
X 13 X O O O O
X 14 O X O O O
X 15 O O X O O
X 16 O O O X O
X 17 O O O O X

9. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

(x,y)∈r if 3 divides x-y

To do this we need to figure out the elements of R
First, don't mix lowercase r and uppercase R. In mathematics, lowercase and uppercase letters often denote different entities.

so we can get our ordered pair.
Which pair? This is the same as saying, "We need to find all students who take this course so that we can find this person."

Those elements are (13,1)(14,2)(15,3)(16,4)(17,5)
Hmm, no (1, 13), (2, 14), (4, 1), (6, 6) and infinitely many other pairs?

with this ordered pair we can fill in our matrix.
You listed 5 pairs and then are saying, "With this ordered pair." Does this make sense?

From the matrix we can see that this is a refelxive relation.
y y y y y y
X 1 2 3 4 5
X 13 X O O O O
X 14 O X O O O
X 15 O O X O O
X 16 O O O X O
X 17 O O O O X
A relation is reflexive when every element is related to itself. Is 1 related to itself or is it related only to 13?

10. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

well im not sure what to tell you but i did it right according to my professor, i'm pretty sure an ordered pair is more the one pair.

11. ## Re: help me find the ordered pairs for (x,y)∈r if 3 divides x-y (relations)

i'm pretty sure an ordered pair is more the one pair.
I don't even know how to understand this. Do you mean that an ordered pair consists of several unordered pairs?

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