Minds On

In grades 9 and 10 you learned about linear and quadratic relations. In this course you will broaden your understanding by learning about a group of relations called functions. You will also expand your mathematical vocabulary to include new ways to describe relations, including stating the domain and range, which describe where, on the Cartesian plane, you will see points on the graph of a relation. You will also represent relations using mapping diagrams, graphs and tables of values.

We are going to start by defining the term relation.

After watching the video, take a few minutes to answer the following questions:

  1. Without looking at the video again, can you recall how many ways there are to express a relation? List the ones you remember.
  1. Which ways are most familiar to you?
  1. Which ways are least familiar to you?
  • A relation is an expression that demonstrates the connection (relationship) between two variables: an independent variable (x) and a dependent variable (y).
  • The expression can be in the form of a set of ordered pairs, a mapping diagram, a table of values, a graph, an equation, a description in words, or a rule.

{ ( 0,1 ) ,   ( 1 ,   2 ) ,   ( 2 ,   3 ) ,   ( 3 ,   4 ) ,   ( 4,5 ) }

x y
1 1
2 4
3 9
4 16
5 25

To fix a car, TJ’s Garage charges a base fee of $20, plus $40 for each hour of labour.

Action

Now let’s build up on our knowledge of relations by analyzing the examples below:

Example 1

To fix a car, TJ’s Garage charges a base fee of $20, plus $40 for each hour of labour.

This is an example of a relation because it is a description of the relationship between the total cost to fix a car and the number of hours of labour. This relation can also be expressed in the form of a set of ordered pairs, a mapping diagram, a table of values, a graph, an equation, or a rule.

  

Take a minute to review the different forms for expressing relations. Identify three different forms in which this relation could be expressed.

Suggestions

Example 2

Mina recorded the ages and heights of her cousins and presented the information in the form of a table below.

The table is an example of a relation because it represents the relationship between age and height of each person.

Age Height in centimeters
15 152
15 185
16 155
17 170
17 173
18 185
20 161

Look carefully at the two examples of relations. What is same? What is different?

Definition

A function is a relation where each value of the independent variable x corresponds to only one value of the dependent variable y (no repeated x values, but it’s okay for the y values to be repeated).

Let’s revisit our two examples of relations.

Example 1

To fix a car, TJ’s Garage charges a base fee of $20, plus $40 for each hour of labour.

This is an example of a relation that is also a function because each value of time is mapped onto only one value of total cost.

The total cost depends on the number of hours of labour. Each value of the independent variable (hours of labour) correspond to only one value of the dependent variable (total cost). Therefore, the relation is a function.

The diagram shown here is called a mapping diagram. The number of hours is mapped onto the total cost.

 Two oval shapes beside one another. The one on the left shows numbers 1, 2, 3 and 4, arranged vertically. The one on the right shows numbers 60, 100, 140 and 180, arranged vertically. Arrows point from left to right, connecting the numbers. Arrows start and end, respectively as follows: 1 to 60; 2 to 100; 3 to 140; 4 to 180.

The total cost depends on the number of hours of labour, therefore we can conclude that the independent variable is the number of hours and the dependent variable is the total cost. You can see that each value for the number of hours maps onto only one value for total cost.

Example 2

Mina recorded the ages and heights of her cousins and presented the information in the form of a table below.

This relation is not a function because the age 15 for example is mapped onto two different heights and the same applies to an age of 17. This tells us that one independent value corresponds to more than one dependent value.

Age Height in centimeters
15 152
15 185
16 155
17 170
17 173
18 185
20 161

In conclusion, a relation can be further classified as a function if there is only one value of the dependent variable for each value of the independent variable.

A function in the form of an equation can be expressed using what we call function notation.

  • With function notation, we replace y with f x , read as “ f at x ” or “ f of x
  • f x means “the value of the dependent variable for a specific value of x
  • It means that we are expressing an equation as a function in terms of x
  • It means that y = f x

Take a minute to watch the video below to learn about the advantage of using function notation:

Now let’s re-visit example 1 and make an equation for the function, and then express it using function notation.

What steps should I take?

Let x represent the number of hours of labour and y represent the total cost.

To fix a car, TJ’s Garage charges a base fee of $20, plus $40 for each hour of labour.

This is a linear relationship, which means that the equation will be in the form

y   =   m x   +   b

where y represents the total cost to get a car fixed, m (rate) is the cost per hour, x is the number of hours and b is the base fee

therefore: x and y are variables, so we keep them the same in the general equation

m   =   40 and b   =   20

The equation is y   =   40 x   +   20

To write the equation using function notation, we replace y with f ( x ) .

Therefore, y   =   40 x   +   20 in function notation becomes f x   =   40 x   +   20

What do you think is the meaning of f 3   =   140   ?

f ( 3 ) = 140 means that when x = 3 , y = 140 . If you were to sketch the graph of

f x   =   40 x + 20 , the point (3, 140) is one of the points on the graph.

In example 2, Mina recorded the ages and heights of her cousins and presented the information in the form of a table on the right.

Can we express this relation using function notation?

Age Height in centimeters
15 152
15 185
16 155
17 170
17 173
18 185
20 161

Domain and Range

Key features of all relations are domain and range.

  • the domain is the set of all possible values of the independent variable
  • the range is the set of all possible values of the dependent variable

Let’s use our two examples to practice stating the domain and range

Example 1:

To fix a car, TJ’s Garage charges a base fee of $20, plus $40 for each hour of labour.

The independent variable is time (x) since the total cost depends on the number of hours. In reality, we cannot have negative time, hence we can conclude that the lowest value of time that would make sense in this situation is 0 and the maximum time is unlimited.

The domain for this example can be stated in words or in mathematical symbols:

Domain = {x is an element of the real numbers, such that x is greater than or equal to zero}

Notation
x is an element of real numbers: x R
such that:
x is greater than or equal to zero: x 0
Using symbols, this becomes D = x R x 0

The dependent variable is the total cost ( y ) since the total cost depends on the number of hours. The lowest cost in this situation is $20 since the base fee is $20 and the total cost is unlimited.

The range for this example can be stated as:
Range = { y is an element of real numbers such that, y is greater than or equal to 20}

Notation
y is an element of real numbers: y R
such that:
y is greater than or equal to 20: y 20
Using symbols, this becomes R = y R y 20

Example 2:

Mina recorded the ages and heights of her cousins and presented the information in the form of a table below.

Age Height in centimeters
15 152
15 185
16 155
17 170
17 173
18 185
20 161

The independent variable in this data is age, but this relation is different from the one above because it is limited to 7 specific pairs of points, hence the domain is a list of the ages.

The domain for this example is a list of the ages and the repeated ages should be represented only once and listed from least to greatest.

Domain = {15, 16, 17, 18, 20}

The dependent variable in this data is height, but this relation is different from the one above because it is limited to 7 specific pairs of points, hence the range is a list of the heights.

The range for this example is a list of the heights and the repeated heights should be represented only once and listed from least to greatest.

Range = {152, 155, 161, 170, 173, 185}

Examples

Example 1:

For the following set of ordered pairs: {(-2,5), (0,11), (0,8), (3,0) (4,-1)}

  1. State the domain and range.
  1. Does the relation define a function? Explain your reasoning.

Example 2:

For the following set of ordered pairs: {(13,1), (-2, 5), (-7,4), (3,2) (9,-1)}

  1. State the domain and range.
  1. Does the relation define a function? Explain you reasoning.

Example 3:

For the given table of values

x y
1 1
2 4
3 9
4 16
5 25
  1. State the domain and range.
  1. Does the relation define a function? Explain you reasoning.

Example 4:

For this mapping diagrams:

 Two oval shapes beside one another. The one on the left shows numbers -2, 3, 7 and 12, arranged vertically. The one on the right shows numbers 14, 12 and 11, arranged vertically. Arrows point from left to right, connecting the numbers. Arrows start and end, respectively as follows: -2 to 14; 3 to 11; 7 to 12; 12 to 11.
  1. State the domain and range.
  1. Does the relation define a function? Explain you reasoning.

Example 5:

For this mapping diagram:

 Two oval shapes beside one another. The one on the left shows numbers 5, 1, -3 and -7, arranged vertically. The one on the right shows numbers 2, 3, 7 and 9, arranged vertically. Arrows point from left to right, connecting the numbers. Arrows start and end, respectively as follows: 5 to 2; 5 to 9; 1 to 3; -3 to 7; -7 to 9.
  1. State the domain and range.
  1. Does the relation define a function? Explain you reasoning.


When given a graph, a quick way of determining whether a relation is a function is by carrying out a test called the vertical line test.

You imagine drawing vertical lines anywhere on the given graph. If the relation:

  • is not a function, the vertical line will pass through at least two points on the graph of the relation
  • is a function, the vertical line will pass through only one point on the graph of the relation

Let’s Practice

Question 1:

For the given graph

  1. State the domain and range.
  1. Does the relation define a function? Explain you reasoning.

Question 2:

For the given graph

  1. State the domain and range.
  1. Does the relation define a function? Explain you reasoning.

Question 3:

For the given graph

  1. State the domain and range.
  1. Does the relation define a function? Explain you reasoning.

You can also recognize whether a relation is a function, or not, given its equation.

  1. Linear relations with the general forms below are functions:
    1. Slope y-intercept form: y = m x + b
    2. Standard form: A x + B y = C or A x + B y + C = 0
  1. Quadratic relations with the general forms below are functions:
    1. Standard form: y   =   a x 2   +   b x   +   c
    2. Vertex form: y   =   a ( x     h ) 2 + k
    3. Factored form: y   = a   ( x s ) ( x   t )
  1. Circles with the general forms below are not functions:
    1. Centre at the origin: r 2   =   x 2 +   y 2
    2. Centre at (a, b): r 2 =   x     a 2 +   y     b 2  

Note:

Sometimes it is helpful to rearrange the equation of a relation to assess whether it is a function or not.

Examples:

Use your knowledge of equations to determine if the following relations are functions. Explain your thought process.

  1. y = 4 x + 3
  1. y = 2 x
  1. y = 5 x 2 - 9 x + 20
  1. y = - 11 ( x + 8 ) 2 + 33
  1. y = 33 + 9 ( x - 4 ) 2
  1. y = - 5 ( x - 3 ) ( x + 4 )
  1. 25 = x 2 + y 2
  1. 5 x 2 + 7 y = 8

Practice Questions

Notebook

Complete the questions that follow in your Notebook. When you are done, compare your work to the solutions given. If you have errors, identify them, write about them, and do the question again below your previous set of solutions.

Question 1:

For the function f ( x ) = x 2 + 10 x evaluate each of the following:

  1. f ( 7 )
  1. f ( 2 )   +   f ( 3 )
  1. 2 f ( 4 )

Question 2:

If f ( x )   =   11 x     9 , solve for x if f ( x )   =   2 .



Question 3:

For each of the following, determine whether, or not, the relation is a function. Explain your thought process.

{(1, 4), (2, 8), (3,16), (4,32)}

{(3,0), (2, 13), (3,-9), (5,11)}

 Two oval shapes beside one another. The one on the left shows numbers 3, 5 and 7, arranged vertically. The one on the right shows numbers 9, 25 and 49, arranged vertically. Arrows point from left to right, connecting the numbers. Arrows start and end, respectively as follows: 3 to 9; 5 to 25; 7 to 49
 Two oval shapes beside one another. The one on the left shows numbers 64, 67 and 90, arranged vertically. The one on the right shows numbers 1, 9, 22 and -8, arranged vertically. Arrows point from left to right, connecting the numbers. Arrows start and end, respectively as follows: 64 to 1; 64 to -8; 67 to 9; 90 to 22
x y
1 2
2 5
3 10
4 17
5 26

y = x 2 + 100 x - 200

y = 2 x - 23

625 = x 2  + y 2

Consolidation

Self-Reflection

In this course you are an independent, self-directed learner. Consider this definition of a self-directed learner:

Definition

Self-directed learners are aware of how they learn best. They are confident and know when to ask for support. Self-directed learners set goals and make realistic plans to meet those goals. In other words, they make a commitment to their own learning and take responsibility for it.

As a self-directed learner, track your progress on the following:

I am able to: All the time Most of the time Half the time Struggling
explain the meaning of the terms relation and function.
explain the difference between a relation and a function.
determine whether a relation is a function or not, given: a set of ordered pairs; a mapping diagram; a table of values; using the vertical line test; using my general knowledge about relations.
represent functions algebraically using function notation.
use function notation to determine dependent variables for given independent variables given: a graph; an equation; a table.
explain the meaning of the terms domain and range.
determine the domain and range given: a set of ordered pairs; a mapping diagram; a table of values; a graph; using my general knowledge about relations.

Now take some time to review and reflect on the Learning goals and Success criteria in this Learning activity.

How would you rate your understanding of the concepts from this Learning activity? Check one.

Awesome! Congratulations. You are ready to move on to the Next Steps.

That’s great! Which concept are you concerned with? You are encouraged to go online and search for websites that provide extra practice. There are also websites that might have a video demonstration of a solution to a similar problem.

Do you feel that some of these concepts are just hard concepts to grasp in general? Try to identify specific places where you could work to improve.

Go back and review the examples and exercises. You should also retry the practice questions.

Do you feel that some of these concepts are just hard concepts to grasp in general? Try to identify specific places where you could work to improve. You may want to review foundation skills that were presented in your Grade 10 course.

Try to work through the example and practice problems independently and then compare your solutions to those provided.

Based on your assessment, do you need more review? Additional practice can be found on the Centre for Education in Mathematics and Computing website, or by searching for resources using key words from the success criteria for this learning activity.

Culminating Activity

Part of the evaluation of this course will be in the form of a culminating activity, worth 10% of your final course work.

 A logo which includes a triangle. Inside the triangle is a wavy line towards the bottom representing water. There are three inverted curves to the left above the wavy line. These inverted curves represent mountains. Beside the inverted curves on the right is a circle with rays representing the sun. Underneath the triangle is the phrase “Protect Our Parks”.

Throughout this course, you will learn about different types of functions, transformations and domain and range. For the culminating activity, you will use this knowledge to create a logo or picture that is informative or suggests solutions to problems that are contributing to environmental issues.

This culminating activity is an opportunity for you to showcase your knowledge of different types of functions and relations as well as your knowledge of domain and range.

The scenario

You are interviewing for a job in the marketing department of an environmental agency. As part of the application process you have been asked to develop a logo for an initiative that targets a specific environmental issue. The subject matter is your choice, but you must provide equations and limits to domain and/or range for each so a graphic designer who works for the organization could duplicate your logo.

Your logo or picture could be a way of:

  1. educating people about environmental issues in the world at large;
  2. drawing attention to specific environmental events (e.g. rising sea levels).
  3. suggesting ways to reduce environmental impact.

Read the instructions for this assessment and the rubric that will be used to score it carefully. Pay close attention to the mathematical concepts that must be included. The checklist and rubric should serve as guides as you complete this activity.

Through the culminating activity, you are encouraged to translate your ideas into appropriate actions to make this world a better place. You are also encouraged to use technology to optimize your learning through technological innovations to deepen and transform your learning as you work on this activity.

Instructions

  • Identify the environmental issue that is the focus of your logo.
  • Create a picture or logo using the concepts of transformations, graphing, domain and range that were taught in this course. Use a minimum of four different types of functions as the key elements of your logo. You may also use relations, such as the inverses of functions or circles. Note that, at this point in the course, you have not learned many of these concepts.
  • Your logo must be displayed on a grid that shows the x and y axes with clear scales.

Incomplete example

 The  same logo used above is super imposed on a cartesian plane. A logo which includes a triangle. Inside the triangle is a wavy line towards the bottom representing water. There are three inverted curves to the left above the wavy line. These inverted curves represent mountains. Beside the inverted curves on the right is a circle with rays representing the sun.

First Key Element (Large Tree)

Equation: y = 2 ( x + 4.5 ) 2 + 4.5

Restrictions on the domain: { 7 < x < 3 }

Description of transformations: The parent function, y = x 2 has been stretched vertically by a factor of 2, reflected in the x-axis, translated left 4.5 units and translated up 4.5 units.

Second key element (Sides of the triangle)

Equation 1: y = - x + 15
Restrictions on the domain: { 1 x 22 }

Equation 2: y = x + 13
Restrictions on the domain: { - 19 x 1 }

  • You may create your logo using pencil and paper or the graphing technology of your choice, such as Desmos or GeoGebra.
  • Describe how your logo relates to the issue that you have chosen.

For each element

  • Include an equation that defines it. With the exception of f ( x ) = x , the equation should feature at least three transformations of the associated parent function.

Examples of parent functions are f ( x ) = x , f ( x ) = x 2 , f ( x ) = x , f ( x ) = 1 x , f ( x ) = sin x and f ( x ) = cos x

  • For each equation (with the exception of f ( x ) = x ) describe the effects of each transformation on the parent function.
  • State the domain and range of each function or relation and the restrictions that were applied when constructing the logo. Use correct mathematical language and notation.

Remember: This culminating activity is an opportunity for you to showcase your knowledge of different types of graphs as well as your knowledge of domain and range.

Rubric

The teacher will assess your work using the following rubric. Before submitting your assessment, review the rubric to ensure that you are meeting the success criteria to the best of your ability.

Success Criteria:

  • Displays logo as a well labelled graph
Level 4
80-100%
Level 3
70-79%
Level 2
60-69%
Level 1
50-59%
With high degree of effectiveness With a considerable degree of effectiveness With some degree of effectiveness With limited effectiveness

Success Criteria:

  • Determines 4 equations that model the graphical representations
Level 4
80-100%
Level 3
70-79%
Level 2
60-69%
Level 1
50-59%
With high degree of effectiveness With a considerable degree of effectiveness With some degree of effectiveness With limited effectiveness

Success Criteria:

  • Describes at least three transformations of the parent function
  • Determines domain and range for each transformed function
Level 4
80-100%
Level 3
70-79%
Level 2
60-69%
Level 1
50-59%
With high degree of effectiveness With a considerable degree of effectiveness With some degree of effectiveness With limited effectiveness

Success Criteria:

  • Chooses an issue and describes how the logo relates to the issue
  • Uses mathematical language and notation
Level 4
80-100%
Level 3
70-79%
Level 2
60-69%
Level 1
50-59%
With high degree of effectiveness With a considerable degree of effectiveness With some degree of effectiveness With limited effectiveness