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[link] displays the age of children in years and their corresponding heights. This table displays just some of the data available for the heights and ages of children. We can see right away that this table does not represent a function because the same input value, 5 years, has two different output values, 40 in. and 42 in.

Age in years,   a   (input) 5 5 6 7 8 9 10
Height in inches,   h   (output) 40 42 44 47 50 52 54

Given a table of input and output values, determine whether the table represents a function.

  1. Identify the input and output values.
  2. Check to see if each input value is paired with only one output value. If so, the table represents a function.

Identifying tables that represent functions

Which table, [link] , [link] , or [link] , represents a function (if any)?

Input Output
2 1
5 3
8 6
Input Output
–3 5
0 1
4 5
Input Output
1 0
5 2
5 4

[link] and [link] define functions. In both, each input value corresponds to exactly one output value. [link] does not define a function because the input value of 5 corresponds to two different output values.

When a table represents a function, corresponding input and output values can also be specified using function notation.

The function represented by [link] can be represented by writing

f ( 2 ) = 1 , f ( 5 ) = 3 , and  f ( 8 ) = 6

Similarly, the statements

g ( 3 ) = 5 , g ( 0 ) = 1 , and  g ( 4 ) = 5

represent the function in [link] .

[link] cannot be expressed in a similar way because it does not represent a function.

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Does [link] represent a function?

Input Output
1 10
2 100
3 1000

yes

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Finding input and output values of a function

When we know an input value and want to determine the corresponding output value for a function, we evaluate the function. Evaluating will always produce one result because each input value of a function corresponds to exactly one output value.

When we know an output value and want to determine the input values that would produce that output value, we set the output equal to the function’s formula and solve for the input. Solving can produce more than one solution because different input values can produce the same output value.

Evaluation of functions in algebraic forms

When we have a function in formula form, it is usually a simple matter to evaluate the function. For example, the function f ( x ) = 5 3 x 2 can be evaluated by squaring the input value, multiplying by 3, and then subtracting the product from 5.

Given the formula for a function, evaluate.

  1. Replace the input variable in the formula with the value provided.
  2. Calculate the result.

Evaluating functions at specific values

Evaluate f ( x ) = x 2 + 3 x 4 at

  1. 2
  2. a
  3. a + h
  4. f ( a + h ) f ( a ) h

Replace the x in the function with each specified value.

  1. Because the input value is a number, 2, we can use simple algebra to simplify.
    f ( 2 ) = 2 2 + 3 ( 2 ) 4 = 4 + 6 4 = 6
  2. In this case, the input value is a letter so we cannot simplify the answer any further.
    f ( a ) = a 2 + 3 a 4
  3. With an input value of a + h , we must use the distributive property.
    f ( a + h ) = ( a + h ) 2 + 3 ( a + h ) 4 = a 2 + 2 a h + h 2 + 3 a + 3 h 4
  4. In this case, we apply the input values to the function more than once, and then perform algebraic operations on the result. We already found that
    f ( a + h ) = a 2 + 2 a h + h 2 + 3 a + 3 h 4

    and we know that

    f ( a ) = a 2 + 3 a 4

    Now we combine the results and simplify.

    f ( a + h ) f ( a ) h = ( a 2 + 2 a h + h 2 + 3 a + 3 h 4 ) ( a 2 + 3 a 4 ) h                           = 2 a h + h 2 + 3 h h                           = h ( 2 a + h + 3 ) h Factor out  h .                           = 2 a + h + 3 Simplify .
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Questions & Answers

a colony of bacteria is growing exponentially doubling in size every 100 minutes. how much minutes will it take for the colony of bacteria to triple in size
Divya Reply
I got 300 minutes. is it right?
Patience
no. should be about 150 minutes.
Jason
It should be 158.5 minutes.
Mr
ok, thanks
Patience
what is the importance knowing the graph of circular functions?
Arabella Reply
can get some help basic precalculus
ismail Reply
What do you need help with?
Andrew
how to convert general to standard form with not perfect trinomial
Camalia Reply
can get some help inverse function
ismail
Rectangle coordinate
Asma Reply
how to find for x
Jhon Reply
it depends on the equation
Robert
whats a domain
mike Reply
The domain of a function is the set of all input on which the function is defined. For example all real numbers are the Domain of any Polynomial function.
Spiro
foci (–7,–17) and (–7,17), the absolute value of the differenceof the distances of any point from the foci is 24.
Churlene Reply
difference between calculus and pre calculus?
Asma Reply
give me an example of a problem so that I can practice answering
Jenefa Reply
x³+y³+z³=42
Robert
dont forget the cube in each variable ;)
Robert
of she solves that, well ... then she has a lot of computational force under her command ....
Walter
what is a function?
CJ Reply
I want to learn about the law of exponent
Quera Reply
explain this
Hinderson Reply
what is functions?
Angel Reply
A mathematical relation such that every input has only one out.
Spiro
yes..it is a relationo of orders pairs of sets one or more input that leads to a exactly one output.
Mubita
Is a rule that assigns to each element X in a set A exactly one element, called F(x), in a set B.
RichieRich
If the plane intersects the cone (either above or below) horizontally, what figure will be created?
Feemark Reply

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Source:  OpenStax, Precalculus. OpenStax CNX. Jan 19, 2016 Download for free at https://legacy.cnx.org/content/col11667/1.6
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