Functions.ppt

4-3 Functions
•A relation is a function provided there is exactly
one output for each input.
•It is NOT a function if one input has more than
one output

INPUT
(DOMAIN)
OUTPUT (RANGE)
FUNCTION
MACHINE
In order for a relationship to be a function…
EVERY INPUT MUST HAVE AN OUTPUT
TWO DIFFERENT INPUTS CAN HAVE THE
SAME OUTPUT
Functions
ONE INPUT CAN HAVE ONLY ONE
OUTPUT

Example 6
No two ordered pairs can have the
same first coordinate
(and different second coordinates).
Which of the following relations are
functions?
R= {(9,10), (-5, -2), (2, -1), (3, -9)}
S= {(6, a), (8, f), (6, b), (-2, p)}
T= {(z, 7), (y, -5), (r, 7), (z, 0), (k, 0)}

Identify the Domain and Range. Then
tell if the relation is a function.
Input Output
-3 3
1 1
3 -2
4
Domain = {-3, 1,3,4}
Range = {-2,1,3}
Function?
Yes: each input is mapped
onto exactly one output

Input Output
-3 3
1 -2
4 1
4
Identify the Domain and Range. Then
tell if the relation is a function.
Domain = {-3, 1,4}
Range = {3,-2,1,4}
Function?
No: input 1 is mapped onto
Both -2 & 1
Notice the set notation!!!

1. {(2,5) , (3,8) , (4,6) , (7, 20)}
2. {(1,4) , (1,5) , (2,3) , (9, 28)}
3. {(1,0) , (4,0) , (9,0) , (21, 0)}

The Vertical Line Test
If it is possible for a vertical line
to intersect a graph at more
than one point, then the graph
is NOT the graph of a function.
Page 117

(-3,3)
(4,4)
(1,1)
(1,-2)
Function?
No, Two points are on
The same vertical line.
Use the vertical line test to visually check if the
relation is a function.

(-3,3)
(4,-2)
(1,1)
(3,1)
Use the vertical line test to visually check if the
relation is a function.
Function?
Yes, no two points are
on the same vertical line

Examples
I’m going to show you a series of
graphs. **don’t write 
Determine whether or not these
graphs are functions.
You do not need to draw the graphs in
your notes. **or write this note

)
(x
f
“f of x”
Input = x
Output = f(x) = y
Function Notation

y = 6 – 3x
-2
-1
0
1
2
12
9
6
0
3
x y
f(x) = 6 – 3x
-2
-1
0
1
2
12
9
6
0
3
x f(x)
Before… Now…
(x, y)
(input, output)
(x, f(x))

Example.
f(x) = 2x2 – 3
Find f(0), f(-3), f(5).

Finding the Domain of a
Function
 When a function is defined by an equation
and the domain of the function is not
stated, we assume that the domain is
All Real Numbers
 There will be certain cases where specific
numbers cannot be included in the domain
or a set of numbers cannot be included in
the domain

Examples…
 f(x) = 2x – 5
*there would be no restrictions on this, so the
domain is All Real Numbers
 g(x) = 1
x – 2
*a denominator cannot equal 0, so x ≠ 2.
The domain is {x | x ≠ 2}
 h(x) = √x + 6
*you cannot take the square root of a
negative number, so x must be ≥ -6. The domain
is {x | x ≥ -6}

Your Turn…Find the domain of
each function
 f(x) = x2 + 2
 g(x) = √x – 1
 h(x) = 1
x + 5

Functions.ppt

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