Any Math Majors? Need discrete mathamatics help..

I

ifoam

New member
If A = {1, 2, 3} and B = {4, 5}, then {<1, 4>, <2, 5>, <3, 5>}, for example, is a binary relation from A to B.

However, {<1, 1>, <1, 4>, <3, 5>} is not a binary relation from A to B because 1 is not in B.



I don't understand why the first part is true. Why are <1,5> <2,4> and <3,4> not included in the relation?



I DO understand the second part. Since a binary relation from a set A to a set B is a set of ordered pairs <a, b> where a is an element of A and b is an element of B.



Anyone have any insite?
 
ifoam said:
If A = {1, 2, 3} and B = {4, 5}, then {<1, 4>, <2, 5>, <3, 5>}, for example, is a binary relation from A to B.

However, {<1, 1>, <1, 4>, <3, 5>} is not a binary relation from A to B because 1 is not in B.



I don't understand why the first part is true. Why are <1,5> <2,4> and <3,4> not included in the relation?



I DO understand the second part. Since a binary relation from a set A to a set B is a set of ordered pairs <a, b> where a is an element of A and b is an element of B.



Anyone have any insite?
Click to expand...

<1,5> <2,4> and <3,4> are not included in the relation because that's the way the relation is defined. <1,5> <2,4> and <3,4> could be included, but that would be a different relation. By the way, the relation as defined is a function from A to B.
 
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