1. Representing Proportional Relationships
Essential Question?
How can you use tables, graphs, mapping diagrams, and equations to represent proportional situations?
8.EE.6, 8.F.1

2. Common Core Standard: 8.F.1 ─ Define, evaluate, and compare functions.
Understand that a function is a rule that assigns to each input exactly one output. The graph of a function is the set of ordered pairs consisting of an input and the corresponding output.
8.EE.6 ─ Understand the connections between proportional relationships, lines, and linear equations.
Use similar triangles to explain why the slope m is the same between any two distinct points on a non-vertical line in the coordinate plane; derive the equation y=mx for a line through the origin and the equation y=mx+b for a line intercepting the vertical axis at b.

3. Objectives:
Understand that a function is a rule that assigns to each input exactly one output.
Identify whether a relationship is a function from a diagram, table of values, graph, or equation.

4. Curriculum Vocabulary
Function (función):
A relationship between an independent variable, x, and a dependent variable, y, where each value of x (input) has one and only one value of y (output).
Relation (relación):
Any set of ordered pairs.
Input (entrada):
A number or value that is entered.
Output (salida):
The number or value that comes out from a process.

5. FUNCTIONS Input = 3 Function: Add 2 Output = 5
The diagram below shows the function “add 2.”
Input = 3
Function: Add 2
Output = 5
There is only one possible output for each input.
The function “add 2” is expressed in words.
It can also be:
written as the equation y=x+2
represented by a table of values
represented as a mapping diagram
shown as a graph.

6. IDENTIFYING FUNCTIONS
Look at the following table:
For EACH INPUT THERE IS EXACTLY ONE OUTPUT.
You can notice that there is NO REPETITION in the INPUT column.
This table represents a function.
INPUT
OUTPUT 10 68 13 73 14 75 18 21 74

7. IDENTIFYING FUNCTIONS
Look at the following table:
For EACH INPUT THERE IS MORE THAN ONE OUTPUT.
You can notice that there is REPETITION in the INPUT column.
This table DOES NOT represent a function.
INPUT
OUTPUT 3 9 10 5 25 26 7 49

8. There is a ONE to ONE relationship!
FUNCTIONS
What are some relationships that are functions?
Each coin of American currency is assigned one specific value in dollars. For example, the value of a penny is always $ In this function, an ordered pair relates the name of a coin and its value in dollars.
Coin
Penny
Nickel
Dime
Quarter
Half-Dollar
Dollar Value
0.01
0.05
0.10
0.25
0.50
There is a ONE to ONE relationship!

9. FUNCTIONS
Most mathematical functions include ordered pairs of numbers. For example, a 120-pound person burns about 65 calories per mile while walking. The table below shows how many calories the person would burn walking different numbers of miles.
Miles (input) 1 2 3 4 5 6
Calories (output) 65
130
195
260
325
390
The input is the number of miles walked.
The rule (function) is to multiply the number of miles by 65.
The output is the number of calories burned.

10. There is a ONE to ONE relationship! This represents a FUNCTION!
FUNCTIONS
Let’s examine the following function:
A basketball coach gives the starting players a game jersey. At the same time he measures the players’ heights. This relationship is a function. For each jersey number, he records only one player’s height.
Player’s Jersey Number (input) 10 13 14 18 21
Players height in inches (output) 68 73 75 74
There is a ONE to ONE relationship!
This represents a FUNCTION!

11. FUNCTIONS What are some relationships that are not functions?
Let’s REVERSE the input and output from the previous table:
Players height in inches (input) 68 73 75 74
Player’s Jersey Number (output) 10 13 14 18 21
Notice there is REPETION IN THE INPUT.
The input 68 has more than one output.
There is NOT a ONE to ONE relationship!
THIS IS NOT A FUNCTION!

12. REPRESENTING FUNCTIONS
There are 4 (FOUR) ways to represent a function that we will explore:
TABLE
MAPPING DIAGRAM
EQUATION
GRAPH

13. REPRESENTING FUNCTIONS
Player’s Jersey Number (input) 10 13 14 18 21
Players height in inches (output) 68 73 75 74
We have already seen how we can represent a relationship using a table. Now let’s create a MAPPING DIAGRAM.
Input: Jersey Number Output: Height 10 13 14 18 21 68 73 74 75

14. REPRESENTING FUNCTIONS
When we reversed the input and output we already discovered that the new relationship is not a function.
Players height in inches (input) 68 73 75 74
Player’s Jersey Number (output) 10 13 14 18 21
Input: Height Output: Jersey Number 68 73 74 75 10 13 14 18 21

15. REPRESENTING FUNCTIONS
The third way we can represent a function is by writing an EQUATION.
Let’s examine the following table:
Do you notice a pattern? Do you think you can come up with a rule?
If you can see a pattern that is ALWAYS THE SAME, that means there is a CONSTANT RATE OF CHANGE.
Number of Hours Worked
Money Earned 1 12 2 24 3 36 4 48 5 60

16. PROPORTIONAL RELATIONSHIPS
A PROPORTIONAL RELATIONSHIP is a relationship between two quantities in which the ration of one quantity to the other is CONSTANT.
In this example the change is always $12 earned for every 1 hour worked.
We can set up a fraction:
𝑜𝑢𝑡𝑝𝑢𝑡 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛𝑝𝑢𝑡 𝑐ℎ𝑎𝑛𝑔𝑒 or 𝑦 𝑥
In this example it would be:
12 1 or 12
Number of Hours Worked
Money Earned 1 12 2 24 3 36 4 48 5 60 12 1 12 1 12 1 12 1

17. PROPORTIONAL RELATIONSHIPS
A PROPORTIONAL RELATIONSHIP can be described by an equation in the form 𝒚=𝒌𝒙, where 𝒌 is a number called the CONSTANT OF PROPORTIONALITY.
If 𝒚=𝒌𝒙, then 𝒌= 𝒚 𝒙
In our example the constant of proportionality, k, is or 12 .
The equation would be:
𝒚= 𝟏𝟐 𝟏 𝒙 𝒐𝒓 𝒚=𝟏𝟐𝒙
Number of Hours Worked
Money Earned 1 12 2 24 3 36 4 48 5 60 12 1 12 1 12 1 12 1

18. PROPORTIONAL RELATIONSHIPS
It is important to note that all PROPORTIONAL RELATIONSHIPS MUST contain the ordered pair (0,0) [the origin] as part of the table. If (0,0) does not appear, the function is NOT proportional.
Be careful to EXTEND THE TABLE, to be sure.
Example: Does the table represent a proportional relationship?
Is there a constant rate of change?
Do you see (0,0) on the table?
Input 2 4 6 8 10
Output 5 15 20 25

19. PROPORTIONAL RELATIONSHIPS There IS a constant rate of change!
Let’s see if there is a constant rate of change. -2 -2 -2 -2
Input 2 4 6 8 10
Output 5 15 20 25 -5 -5 -5 -5
We see that for each time the output decreases by 5, the input decreases by 2.
There IS a constant rate of change!

20. PROPORTIONAL RELATIONSHIPS
Let’s extend the table to see if (0,0) is part of the table.
Input 2 4 6 8 10
Output 5 15 20 25 -2 -2 -2 -2 -2
Input 2 4 6 8 10
Output 5 15 20 25 -5 -5 -5 -5 -5
Now we see that (0,0) is part of the table.
Since there is a constant rate of change and (0,0) is part of the table, this IS PROPORTIONAL.
We can write the equation as 𝑦= −5 −2 𝑥 or 𝑦= 5 2 𝑥

21. PROPORTIONAL RELATIONSHIPS
Does this table represent a proportional relationship?
Input 1 2 3 4 5
Output 9 16 25
Is there a constant rate of change? NO
This is NOT a proportional relationship.

22. PROPORTIONAL RELATIONSHIPS
Does this table represent a proportional relationship?
Input 1 2 3 4 5
Output 15 20 25 30 35
Is there a constant rate of change?
YES
If you extend the table, will (0,0) be part of it? NO
This is NOT a proportional relationship.

23. PROPORTIONAL RELATIONSHIPS
So far we have seen a proportional relationship represented as:
A TABLE
A MAPPING DIAGRAM
An EQUATION
Input
Output 1 3 2 6 9 4 12 5 15 1 2 3 4 5 6 9 12 15
𝑦=3𝑥

24. PROPORTIONAL RELATIONSHIPS
The fourth way to represent a proportional relationsip is as
A GRAPH
The best way to graph a relationship is to use the table.
Create ordered pairs and plot them.
Input
Output 1 3 2 6 9 4 12 5 15
(1,3)
(2,6)
(3,9)
(4,12)
(5,15)

25. REPRESENTING FUNCTIONS
Since we know there is a CONSTANT RATE OF CHANGE, we can connect the dots with a STRAIGHT LINE.

26. PROPORTIONAL RELATIONSHIPS
Let’s examine the graph of a proportional relationship and a non-proportional relationship and see if we can draw a conclusion.
PROPORTIONAL RELATIONSHIP
NON-PROPORTIONAL RELATIONSHIP
Input
Output 1 3 2 6 9 4 12 5 15
Input
Output 1 2 3 4 5 6
What is the main difference between the two graphs?
The graph of a PROPORTIONAL RELATIONSHIP
is a LINE that PASSES THROUGH THE ORIGIN!

27. PROPORTIONAL RELATIONSHIPS
We have now seen a PROPORTIONAL RELATIONSHIP represented as:
A TABLE
CONSTANT rate of change
CONTAINS the ordered pair (0,0)
A MAPPING DIAGRAM
Shows a ONE to ONE relationship
An EQUATION
Takes the form 𝑦=𝑘𝑥 where 𝑘 is the constant of proportionality
A GRAPH
A LINE that passes through the ORIGIN
Input
Output 1 3 2 6 9 4 12 5 15 1 2 3 4 5 6 9 12 15
𝑦=3𝑥