Thursday, May 2, 2013

Relations and Functions Math

Introduction to relations and functions math:
When comparing (relate) the objects (human beings) the concept of relation becomes very important. In a similar fashion we connect two sets (set of objects) by means of relation. A function math is a one of the type of relation. In a function, number two ordered pairs can have the same first element and a different second element. That is, for functions, corresponding to every 1st element of the ordered pairs, there must be a different 2nd element. The relations and functions math example problems and practice problems are given below.

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Example problems for relations and functions math:


Example problem 1:

A function f from N`->` N is defined by f(x) = 7x. Find the range of function

Solution:

The range of f: N ? N is the set of all images of f(x) = 7x, for x = 1, 2, 3, ? N.

The range of f = {7, 14, 21, 28, …}.

Example problem 2:

Let A = {1, 2}, B = {a, b}. Find some relations from A ? B and B ? A.

Solution:

Since relation from A to B is a subset of the Cartesian product

A × B = {(1 , a) , (1, b) , (2 , a) , (2 , b)} any subset of A × B is a relation from A ? B.

{(1 , a), (1 , b), (2 , a), (2 , b)}, {(1, a), (1, b)}, {(1, b, (2, b)}, {(1 , a)} are some relations from A to B.

Similarly any subset of B × A = {(a , 1), (a , 2), (b , 1), (b , 2)} is a relation from B to A.

{(a , 1), (a , 2), (b , 1), (b , 2)}, {(a, 1), (b, 1)}, {(a, 2), (b, 1)} are some relations from B to A.

Example problem 3:

A relation R is defined on the set {–2, 0, 1, 2, 3, 5} as R = {(–2,1), (3,0), (2,5)}. Write down the domain and the range of R.

Solution:

Domain of R is the set of all 1st elements of the ordered pairs in R

Domain = {–2, 3, 2}

Range of R is the set of all 2nd elements of the ordered pairs in R.

Range = {1, 0, 5}.

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Practice problems for relations and functions math:


Practice problem 1:

In the set N of natural numbers, define the relation R by x Ry if x + y = 9. Find n(R).

Answer: R = {(1,8), (2,7), (3,6), (4,5), (5,4), (6,3), (7,2), (8,1)} and n(R) = 8.

Practice problem 2:

Let I be the set of integers. R on I is defined as a R b if a – b is an even integer. Prove that R is an equivalence relation.

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