How to Identify Relations that are not Functions

Oct 13, 2025 by wbrum.org 73 views

Introduction

In mathematics, a relation is a set of ordered pairs that describe the relationship between two sets of values. A function, on the other hand, is a special type of relation where each input value corresponds to exactly one output value. In this article, we will explore the concept of relations and functions, and learn how to identify which relations are not functions.

What is a Relation?

A relation is a set of ordered pairs that describe the relationship between two sets of values. For example, consider the relation R = {(1, 2), (2, 3), (3, 4), (4, 5)}. This relation describes the relationship between the set of numbers {1, 2, 3, 4} and the set of numbers {2, 3, 4, 5}.

What is a Function?

A function is a special type of relation where each input value corresponds to exactly one output value. In other words, for every input value, there is only one output value. For example, consider the function f(x) = 2x. This function takes an input value x and returns an output value that is twice the input value.

How to Identify Relations that are not Functions

To identify relations that are not functions, we need to look for relations where each input value corresponds to more than one output value. In other words, we need to look for relations where there are multiple ordered pairs with the same input value but different output values.

Example 1: A Relation that is not a Function

Consider the relation R = {(1, 2), (1, 3), (2, 4), (3, 5)}. This relation describes the relationship between the set of numbers {1, 2, 3} and the set of numbers {2, 3, 4, 5}. However, this relation is not a function because the input value 1 corresponds to two different output values, 2 and 3.

Example 2: A Relation that is a Function

Consider the relation R = {(1, 2), (2, 3), (3, 4), (4, 5)}. This relation describes the relationship between the set of numbers {1, 2, 3, 4} and the set of numbers {2, 3, 4, 5}. This relation is a function because each input value corresponds to exactly one output value.

Example 3: A Relation that is not a Function

Consider the relation R = {(1, 2), (1, 3), (1, 4), (2, 5), (3, 6)}. This relation describes the relationship between the set of numbers {1, 2, 3} and the set of numbers {2, 3, 4, 5, 6}. However, this relation is not a function because the input value 1 corresponds to three different output values, 2, 3, and 4.

Example 4: A Relation that is a Function

Consider the relation R = {(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)}. This relation describes the relationship between the set of numbers {1, 2, 3, 4, 5} and the set of numbers {2, 3, 4, 5, 6}. This relation is a function because each input value corresponds to exactly one output value.

Conclusion

In conclusion, a relation is a set of ordered pairs that describe the relationship between two sets of values. A function is a special type of relation where each input value corresponds to exactly one output value. To identify relations that are not functions, we need to look for relations where each input value corresponds to more than one output value. By understanding the concept of relations and functions, we can better analyze and solve mathematical problems.

Selecting Relations that are not Functions

Now that we have learned how to identify relations that are not functions, let's apply this knowledge to the given problem. We are given the following relations:

$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right)\right\}$
$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$
$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$

We need to select the relations that are not functions.

Relation 1

Let's analyze the first relation:

$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right)\right\}$

This relation is not a function because the input value $-\frac{1}{2}$ corresponds to two different output values, $\frac{3}{4}$ and $-\frac{3}{4}$ .

Relation 2

Let's analyze the second relation:

$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$

This relation is not a function because the input value $-\frac{1}{2}$ corresponds to two different output values, $-\frac{3}{4}$ and $\frac{3}{4}$ .

Relation 3

Let's analyze the third relation:

$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$

This relation is not a function because the input value $-\frac{1}{2}$ corresponds to two different output values, $\frac{3}{4}$ and $-\frac{3}{4}$ .

Conclusion

In conclusion, the relations that are not functions are:

$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right)\right\}$
$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$
$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$
Q&A: Relations and Functions in Mathematics =====================================================

Q: What is a relation in mathematics?

A: A relation is a set of ordered pairs that describe the relationship between two sets of values. For example, consider the relation R = {(1, 2), (2, 3), (3, 4), (4, 5)}. This relation describes the relationship between the set of numbers {1, 2, 3, 4} and the set of numbers {2, 3, 4, 5}.

Q: What is a function in mathematics?

A: A function is a special type of relation where each input value corresponds to exactly one output value. In other words, for every input value, there is only one output value. For example, consider the function f(x) = 2x. This function takes an input value x and returns an output value that is twice the input value.

Q: How do I identify relations that are not functions?

A: To identify relations that are not functions, you need to look for relations where each input value corresponds to more than one output value. In other words, you need to look for relations where there are multiple ordered pairs with the same input value but different output values.

Q: What are some examples of relations that are not functions?

A: Here are a few examples of relations that are not functions:

$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right)\right\}$
$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$
$\left\{\left(-\frac{1}{5}, \frac{1}{4}\right),\left(-\frac{1}{4},-\frac{1}{8}\right),\left(\frac{1}{4}, \frac{1}{5}\right),\left(-\frac{1}{2}, \frac{3}{4}\right),\left(-\frac{1}{2}, -\frac{3}{4}\right)\right\}$

Q: How do I determine if a relation is a function or not?

A: To determine if a relation is a function or not, you need to check if each input value corresponds to exactly one output value. If there are multiple ordered pairs with the same input value but different output values, then the relation is not a function.

Q: What are some common mistakes to avoid when working with relations and functions?

A: Here are a few common mistakes to avoid when working with relations and functions:

Not checking if each input value corresponds to exactly one output value.
Not recognizing that a relation can have multiple ordered pairs with the same input value but different output values.
Not understanding the difference between a relation and a function.

Q: How do I apply the concept of relations and functions to real-world problems?

A: The concept of relations and functions can be applied to a wide range of real-world problems, such as:

Modeling population growth and decline.
Analyzing the relationship between variables in a system.
Predicting the behavior of a system based on its inputs and outputs.

Q: What are some advanced topics related to relations and functions?

A: Some advanced topics related to relations and functions include:

Inverse functions.
Composite functions.
Relations and functions in higher dimensions.

Conclusion

In conclusion, relations and functions are fundamental concepts in mathematics that have numerous applications in real-world problems. By understanding the difference between a relation and a function, and how to identify relations that are not functions, you can better analyze and solve mathematical problems.