2. PRELIMINARIES
Class Schedule
Engagement in Activities
Triad – Learners will form a three member
group.
Incentives
Discipline and Respect
Subject Requirements
Key Result Area’s
Student’s Assignment Monitoring Sheet
4. LEARNING OUTCOMES
Representing Real-life Situations Using
Functions
• Recall the concepts of relations and
functions
• Define and explain functional relationship
as a mathematical model of situation
• Represent real-life situations using
functions, including piece-wise functions
6. Is any set of ordered pairs.
The set of all first elements of
the ordered pairs of the relation.
The set of all second elements.
Relation
Domain
Range
7. .
Is a relation or rule of
correspondence between two
elements (domain and range)
such that each element in the
domain corresponds to exactly
one element in the range.
Function
19. .
A relation between two sets of
numbers can be illustrated by graph in
the Cartesian plane, and that a
function passes the vertical line test.
A graph of a relation is a function if
any vertical line drawn passing
through the graph intersects it at
exactly one point.
23. Which is Which?
Scenario 3: As part of their requirements in Statistics class, Andrei
made a survey on the religion of his classmates and here’s what he
found out.
Andrei: Good morning classmates, as our requirement in Statistics may
I know your religion. This data will be part of my input in the survey that I
am doing.
Ana : I am a Catholic.
Kevin: I am also a Catholic.
Sam: I am a member of the Iglesia ni Cristo.
Joey: I am a Born Again Christian.
Lanie: My family is a Muslim.
Jen: We are sacred a Catholic Family.
Andrei: Thank you classmates for your responses.
Function
25. Real-Life Situations
If height (H) is a function of age (a), give a
function H that can represent the height of a
person in a age, if every year the height is added
by 2 inches.
Solution:
Since every year the height is added by 2 inches,
then the height function is 𝑯(𝒂)=𝒂+2
26. Real-Life Situations
If distance (D) is a function of time (t), give a
function D that can represent the distance a car
travels in t time, if every hour the car travels 60
kilometers.
Solution:
Since every hour, the car travels 60 kilometers,
therefore the distance function is given by 𝑫(𝒕)=𝟔𝟎𝒕
27. Real-Life Situations
Give a function B that can represent the amount
of battery charge of a cellular phone in h hour, if
12% of battery was loss every hour.
Solution:
Since every hour losses 12% of the battery, then the
amount of battery function is 𝑩(𝒉)=𝟏𝟎𝟎−𝟎.𝟏𝟐𝒉
28. Real-Life Situations
Squares of side x are cut from each corner of a 10 in x 8
in rectangle, so that its sides can be folded to make a box
with no top. Define a function in terms of x that can
represent the volume of the box.
Solution:
The length and width of the box are 10 - 2x and 8 - 2x,
respectively. Its height is x. Thus, the volume of the box can
be represented by the function.
𝑽(𝒙) = (𝟏𝟎 − 𝟐𝒙)(𝟖 − 𝟐𝒙)(𝒙) = 𝟖𝟎𝒙 − 𝟑𝟔𝒙𝟐 + 𝟒𝒙𝟑
29. Piecewise Functions
𝑓 𝑥 =
formula 1 if x is in domain 1
formula 2 if x is in domain 2
formula 3 if x is in domain 3
30. Piecewise Functions
A user is charged ₱250.00 monthly for a
particular mobile plan, which includes 200 free
text messages. Messages in excess of 200 are
charged ₱1.00 each. Represent the monthly cost
for text messaging using the function t(m), where
m is the number of messages sent in a month.
𝒕 𝒎 =
𝟐𝟓𝟎 𝒊𝒇 𝟎 < 𝒎 ≤ 𝟐𝟎𝟎
𝟐𝟓𝟎 + 𝒎 − 𝟐𝟎𝟎 𝒊𝒇 𝒎 > 𝟐𝟎𝟎
31. Piecewise Functions
A certain chocolate bar costs ₱50.00 per piece.
However, if you buy more than 5 pieces they will
mark down the price to ₱48.00 per piece. Use a
piecewise function to represent the cost in terms
of the number of chocolate bars bought.
𝑷 𝒄 =
𝟓𝟎 𝒊𝒇 𝟏 < 𝒄 ≤ 𝟓
𝟒𝟖 𝒄 𝒊𝒇 𝒄 > 𝟓
32. Piecewise Functions
The cost of hiring a catering service to serve
food for a party is ₱250.00 per head for 50
persons or less, ₱200.00 per head for 51 to 100
persons, and ₱150.00 per head for more than
100. Represent the total cost as a piecewise
function of the number of attendees to the party.
𝑪 𝒉 =
𝟐𝟓𝟎𝒉 𝒊𝒇 𝒉 ≤ 𝟓𝟎
𝟐𝟎𝟎𝒉 𝒊𝒇 𝟓𝟏 < 𝒉 ≤ 𝟏𝟎𝟎
𝟏𝟎𝟎𝒉 𝒊𝒇 𝒉 > 𝟏𝟎𝟎
35. Homework
1. In three to five sentences, write the
significance of function in showing real-life
situations.
2. Cite 2 real-life situations that show
functions.
36. Performance Task
At home or in your community, look for the at least three (3) situations that
could represent functions. From the identified situations, write a sample
problem and its corresponding function equation.
Example:
Situation: The budget for food is a function of the number of family
members.
Problem: Reyes family has Php ₱1,500.00 food budget for each member of
their family in a month. Express the total food budget (B) as a function of
number of family members (n) in one month.
Function: 𝐵(𝑥)=1500𝑥
37. . o What do you think were the key mathematical concepts
addressed in this lesson?
o Would you rate your level of understanding of the material
covered in this lesson as high, moderate, or low?
o Has the lesson helped you to gain further insight into aspects of
the material covered that represent strengths or represent
weaknesses?
o What would you describe as the main barriers, if any, to your
ongoing progress and achievement in relation to the topic area
addressed in this lesson?
o What do you think would best assist your ongoing progress and
achievement in relation to the topic area?
Welcome to the first lesson of your General Mathematics. This lesson will give you the practical application of functions in a real-life scenario including the piece-wise function. When you are in Grade 8, you already encountered relation and function. But in this module, let’s take into a deeper sense on how this topic can be useful in our daily life. Are you all ready?
Before we proceed in representing real-life scenario using function, let’s go back to where we start. What have you remembered about relations and functions?
Functions can often be used to model real-life situations. Identifying an appropriate functional model will lead to a better understanding of various phenomena.
The above scenarios are all examples of relations that show function. Monogamous marriage (e.g. Christian countries) is an example of function when there is faith and loyalty. Let say, June is the domain and Mae is the range, when there is faithfulness in their marriage, there will be one-to-one relationship - one domain to one range.
Nationality could also illustrate a function. We expect that at least a person has one nationality. Let say Kim is the domain and her nationality is the range, therefore there is a one-to-one relationship. Since Kim was born and live in the Philippines, she can never have multiple nationalities except Filipino. (Remember: Under RA 9225 only those naturally-born Filipinos who have become naturalized citizens of another country can have dual citizenship. This is not applicable to Kim since she was born in the Philippines and never a citizen of other country.)
Religion is also an example of function because a person can never have two religions. Inside the classroom, three classmates said that they are Catholic. This shows a many-to-one relationship. Classmates being the domain and religion being the range indicate that different values of domain can have one value of range. One-to-one relationship was also illustrated by the classmates who said that they are Born Again, Muslim and Iglesia ni Cristo - one student to one religion.
Function can be illustrated as a machine where there is the input and the output. When you put an object into a machine, you expect a product as output after the process being done by the machine. For example, when you put an orange fruit into a juicer, you expect an orange juice as the output and not a grape juice. Or you will never expect to have two kinds of juices - orange and grapes.
You have learned that function can be represented by equation. Since output (y) is dependent on input (x), we can say that y is a function of x. For example, if a function machine always adds three (3) to whatever you put in it. Therefore, we can derive an equation of x + 3 = y or f(x) = x+ 3 where f(x) = y.
There are functions that requires more than one formula in order to obtain the given output. There are instances when we need to describe situations in which a rule or relationship changes as the input value crosses certain boundaries. In this case, we need to apply the piecewise function.
A piecewise function is a function in which more than one formula is used to define the output. Each formula has its own domain, and the domain of the function is the union of all these smaller domains.