All About Functions-
for a Layman
Dr Farhana Shaheen
Definition of a Function
Specific------ Layman
What is the meaning of Function?
An Event? Occasion?
Or???
Where do we use this word “Function”
other than Events?
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A Function is a Relation or a Link between
two sets- X and Y
What is a RELATION?
 A Father – Children Relation
A Children- Father Relation
A Student – Teacher Relation
A Teacher – Student Relation…… and much
more
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Example: A Father – Children Relation
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A Function is a Relation or a Link between
two sets- X and Y, such that
Each element of X has a unique element
(image) in Y.
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Let’s Go for Ice Creams…
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Three friends A, B and C plan to have Ice Cream
Treat- The condition is EVERYONE Must Choose
Only one Ice-Cream
 A
B
C
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Suppose that A chooses two, B chooses one and
C refuse to have any- Rules violated?
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Three friends A, B and C plan to have Ice Cream
Treat- The condition is EVERYONE Must Choose
Only one Ice-Cream
 A
B
C
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Function is an Input-Output Machine
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Note: The Output DEPENDS upon
the Input. Input is INDEPENDENT.
But Input depends upon the MACHINE.
Examples of Functions as Machines
Every Machine has a Program
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A Function is an Input-Output Machine
y = f(x) (x, y are Dummy variables)
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Definition: Function
A Function is a rule (or relation) from a set X to a set
Y such that each element of X has a unique element
in Y. We denote it by y = f(x).
The set X is called the Domain and Y is called the Co-
domain.
Set X is Independent and Y is Dependent.
Each → Elements of Domain are not missed
Unique → Elements of Domain are not repeated
DOMAIN is Very Important
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Dependent and Independent Variables
Examples of Functions in one, two or more variables:
Area of a Circle depends upon its Radius
A(r) = 𝜋𝑟2
Area of a Rectangle depends upon its length
and width. A(L,W) = LW
Volume of a Cuboid depends upon its length,
width and height. V(L,W,H) = LWH
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Example: Three friends A, B, C, plan to have ice-
creams. Suppose all of them choose Chocolate
Ice-Cream. Rules violated?
 X → Y
A
B
C
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Example: Three friends A, B, C, plan to have ice-
creams. Suppose each of them choose different Ice-
Cream. What is this function called?
 X → Y
A
B
C
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Are these Functions or Relations?
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Representing Functions as set of Ordered
pairs f = {(a, b), (c, d)}
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Graphs of Functions
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A graphic illustration conveys a
stronger message than words
—one picture is worth a thousand
words.
To draw a Graph….. We Need to know its
DOMAIN
Why is it necessary to find the
Domain of a Function?
Where to begin with….
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Concept of Domain and Range
What is the difference between Co-domain and
Range?
Let my machine is Programmed to square every
Input, and add 3 more units.
So f(x) = 𝒙𝟐
+ 𝟑.
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f(x) should be DEFINED on its Domain
A function is said to be DEFINED on the Domain if its
image exists on its values, and is not imaginary. i.e.
images are real-valued.
For example:
f(x)=
1
𝑥 −3
does not exist at x = 3.
Also f(x) = 𝑥 + 5 has imaginary values for x < -5.
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STORY OF IOTA
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Depends on the
type of function
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Finding domain and Range from graph
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Finding domain and Range from graph
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Note: Not every graph is the graph of a
function-
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Vertical Line Test for a Graph to be the
graph of a Function
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Types of Functions
 Linear Function Log Function
 Polynomial Function Exponential Function
 Radical Function Rational Function
 Identity Function
 Constant Function
 Reciprocal Function
 Trigonometric Function
 Inverse Trigonometric Function
 Piecewise Function
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Constant Function y= k.
What is x =?
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Reciprocal Functions
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Reciprocal Functions
y =
1
𝑥2
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Polynomial Functions vs Reciprocal Functions
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Radical Functions
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Piecewise Functions
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Exponential Functions y = 𝑎𝑥
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EXAMPLE: EXPONENTIAL FUNCTIONS
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Logarithmic Functions y = log x /lnx
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Bracket Functions (Step Curve)
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BRACKET FUNCTIONS
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Trigonometric Functions
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Hyperbolic Functions
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DESMOS:
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All About Functions- For a Layman.pptx