algebra 4.8 functions and relations functions and relations a relation is a set of ordered pairs a...
TRANSCRIPT
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Algebra
4.8 Functions and Relations
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Functions and Relations A relation is a set of ordered pairs A function is a rule that establishes
a relationship between two quantities, called the input and the output.
Input = x The collection of the x values is known as the domain.
Output = y. The collection of the y values is known as the range.
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Function
The most important part of the function: every input has only one output. An x cannot have two y’s.
Examples:x y
1
2
3
4
2
4
4
5
Is this relation a function?
Yes. Each input has only one output.
x y
1
1
2
3
5
7
8
9
Is this relation a function?
No. The input 1 has Two outputs 5 and 7.
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A Birthday Example
Imagine this relation: Input = All the students at CHSFA Output = The Birthday of that
Student Is this a function?
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Let’s See
Person Birthday
Jessica Jones May 5th
Bob Boone June 21st
Sally Smith Nov. 18th
Todd Thomas Nov. 18th
Is this a function?
Does each input have only one output?
Similarly, does each person have only one birthday?
Since each input has only one output, then this is a function.Todd Thomas April 3rd
This would make this not a function because an input (Todd Thomas) would have more than one Output (Nov. 18th and April 3rd). This cannot happen.
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What if the input were the days of the year and the output
was the people who had that day as their birthday? Let’s try as a class.
DatePeople’sB-Day
Jan. 1st Stu Sanders
Jan. 2nd Lyn Lewis
Jan. 3rd John Jacobs
Jan. 3rd Sally Struthers
Is this a function?
Does each input have only one output?
Similarly, does each date have only one person celebrating that day as their birthday?
No. Since there is an input that has more than one output, then this is not a function.
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Vertical Line Test
A relation is a function if its graph passes the vertical line test. All vertical lines must intersect the graph only once.
Are these functions? Do they pass the vertical line test?
Yes! No! No! Yes!
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Evaluate the Following Function in Function Notation
f(x) = 2x – 3 when x = -2 f(-2) = 2(-2) – 3 = -4 – 3
= -7
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You try! Evaluate the Following Function in Function Notation…
f(x) = -7x – 3 when x = 4 f(4) = -7(4) – 3 = -28 – 3
= -31
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Graphing a Function
Graph f(x) = -1/2x + 4 Replace f(x) with y Graph y = -1/2x + 4
(0, 4)
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Is the relation a function? If yes, state the domain and range.
x y
1
2
3
4
-2
-3
-3
-5
Yes, the relation is a function!
The domain is 1, 2, 3, and 4
The range is -2, -3, -3, -5
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Real-world functions
Coke machine Toaster Lets come up with a few as a class.
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Function
Function- exactly one output for one input.
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Function Rule
Function Rule- equation that describes a functional relationship. X= total cokes 1= price per coke N= number of cokes needed
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Writing a function rule
# of loads
1 2 3 4
Cost $2.75 $5.50 $8.25 $11.00
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# of loads
1 2 3 4
Cost $2.75 $5.50 $8.25 $11.00
Find the difference between each box
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Put into fraction form and divide
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Plug into equation
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Check it...
# of loads
1 2 3 4
Cost $2.75 $5.50 $8.25 $11.00
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What if it doesn’t work?
TimeCost of Bike Rental
1 $10
2 $16
3 $22
4 $28
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What if it doesn’t work???
TimeCost of Bike Rental
1 $10
2 $16
3 $22
4 $28
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What do I need to add?
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The Rule is. Check it with another number.
Time Cost
1 $10
2 $16
3 $22
4 $28
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