"f(x) = ... " is the classical method of writing a role. And tbelow are other methods, as you will certainly see!

Input, Relationship, Output

We will check out many kind of ways to think about features, but there are always 3 main parts:

The input The partnership The output
Input Relationship Output
0 × 2 0
1 × 2 2
7 × 2 14
10 × 2 20

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... ...

But we are not going to look at specific attributes ... ... instead we will look at the basic idea of a function.


First, it is helpful to offer a role a name.

The a lot of widespread name is "f", however we can have actually various other names choose "g" ... or also "marmalade" if we desire.

But let"s use "f":


We say "f of x equates to x squared"

what goes into the function is put inside parentheses () after the name of the function:

So f(x) shows us the feature is dubbed "f", and "x" goes in

And we typically view what a duty does via the input:

f(x) = x2 reflects us that attribute "f" takes "x" and also squares it.

Example: with f(x) = x2:

an input of 4 becomes an output of 16.

In fact we have the right to write f(4) = 16.

The "x" is Just a Place-Holder!

Don"t acquire also pertained to about "x", it is just tbelow to show us wbelow the input goes and also what happens to it.

It can be anything!

So this function:

f(x) = 1 - x + x2

Is the very same attribute as:

f(q) = 1 - q + q2 h(A) = 1 - A + A2 w(θ) = 1 - θ + θ2

The variable (x, q, A, etc) is just tbelow so we understand wbelow to put the values:

f(2) = 1 - 2 + 22 = 3

Sometimes Tright here is No Function Name

Sometimes a function has actually no name, and also we view somepoint like:

y = x2

But there is still:

an input (x) a connection (squaring) and also an output (y)


At the optimal we shelp that a role was like a maker. But a function doesn"t really have belts or cogs or any relocating parts - and it doesn"t actually damage what we put into it!

A function relates an input to an output.

Saying "f(4) = 16" is like saying 4 is somehow related to 16. Or 4 → 16


Example: this tree grows 20 cm annually, so the elevation of the tree is related to its age making use of the attribute h:

h(age) = age × 20

So, if the age is 10 years, the height is:

h(10) = 10 × 20 = 200 cm

Here are some instance values:

ageh(age) = age × 20

What Types of Things Do Functions Process?

"Numbers" appears an apparent answer, yet ...


... which numbers?

For example, the tree-elevation feature h(age) = age×20 provides no feeling for a period much less than zero.

... it might likewise be letters ("A"→"B"), or ID codes ("A6309"→"Pass") or stranger points.

So we need something more powerful, and that is wbelow sets come in:


A collection is a collection of things.

Here are some examples:

Set of even numbers: ..., -4, -2, 0, 2, 4, ...Set of clothes: "hat","shirt",... Set of prime numbers: 2, 3, 5, 7, 11, 13, 17, ...Hopeful multiples of 3 that are less than 10: 3, 6, 9

Each individual point in the set (such as "4" or "hat") is called a member, or element.

So, a role takes elements of a set, and offers ago facets of a set.

A Function is Special

But a role has unique rules:

It must occupational for every feasible input value And it has just one relationship for each input worth

This can be said in one definition:


Formal Definition of a Function

A feature relates each element of a setthrough precisely one facet of anotherset(possibly the same set).

The Two Important Things!


"...each aspect..." suggests that eincredibly facet in X is concerned some facet in Y.

We say that the feature covers X (relates eexceptionally facet of it).

(But some aspects of Y might not be regarded at all, which is fine.)


"...exactly one..." means that a function is single valued. It will certainly not offer earlier 2 or even more results for the same input.

So "f(2) = 7 or 9" is not right!

"One-to-many" is not allowed, yet "many-to-one" is allowed:

(one-to-many) (many-to-one)
This is NOT OK in a function But this is OK in a function

When a relationship does not follow those two rules then it is not a function ... it is still a relationship, simply not a duty.

Example: The connection x → x2


Could also be composed as a table:

X: x Y: x2
3 9
1 1
0 0
4 16
-4 16
... ...

It is a function, because:

Eincredibly element in X is related to Y No element in X has actually two or more relationships

So it follows the rules.

(Notice how both 4 and -4 relate to 16, which is allowed.)

Example: This relationship is not a function:


It is a relationship, yet it is not a function, for these reasons:

Value "3" in X has no relation in Y Value "4" in X has no relation in Y Value "5" is regarded more than one worth in Y

(But the fact that "6" in Y has actually no relationship does not matter)


Vertical Line Test

On a graph, the concept of single valued suggests that no vertical line ever crosses more than one value.

If it crosses even more than once it is still a valid curve, yet is not a function.

Some forms of features have actually stricter rules, to find out even more you deserve to check out Injective, Surjective and Bijective

Infinitely Many

My examples have simply a few values, however attributes commonly occupational on sets with infinitely many facets.

Example: y = x3

The output collection "Y" is additionally all the Real Numbers

We can not present ALL the values, so here are simply a couple of examples:

X: x Y: x3
-2 -8
-0.1 -0.001
0 0
1.1 1.331
3 27
and so on... and also so on...

Doprimary, Codoprimary and Range

In our examples above

the set "X" is called the Domain
, the collection "Y" is called the Codomain, and also the collection of facets that acquire pointed to in Y (the actual worths produced by the function) is dubbed the Range.

We have a distinct page on Domain, Range and also Codomain if you desire to recognize even more.

So Many type of Names!

Functions have been provided in mathematics for a very long time, and also numerous various names and also means of composing features have actually come around.

Here are some common terms you should acquire familiar with:


Example: z = 2u3:

"u" might be called the "independent variable" "z" could be dubbed the "dependent variable" (it relies on the worth of u)

Example: f(4) = 16:

"4" might be referred to as the "argument""16" could be dubbed the "worth of the function"

Example: h(year) = 20 × year:


h() is the function"year" could be referred to as the "argument", or the "variable"a fixed worth choose "20" have the right to be called a parameter

We frequently contact a role "f(x)" once in reality the function is really "f"

Ordered Pairs

And below is an additional way to think about functions:

Write the input and output of a role as an "ordered pair", such as (4,16).

They are called ordered pairs bereason the input constantly comes first, and also the output second:

(input, output)

So it looks like this:

( x, f(x) )


(4,16) suggests that the feature absorbs "4" and also gives out "16"

Set of Ordered Pairs

A attribute can then be characterized as a set of ordered pairs:

Example: (2,4), (3,5), (7,3) is a role that states

"2 is concerned 4", "3 is related to 5" and "7 is associated 3".

Also, notice that:

the domain is 2,3,7 (the input values) and also the range is 4,5,3 (the output values)

But the function has to be single valued, so we likewise say

"if it consists of (a, b) and (a, c), then b should equal c"

Which is simply a way of saying that an input of "a" cannot produce 2 various outcomes.

Example: (2,4), (2,5), (7,3) is not a duty because 2,4 and 2,5 indicates that 2 could be pertained to 4 or 5.

In other words it is not a duty bereason it is not single valued


A Benefit of Ordered Pairs

We can graph them...

... because they are also coordinates!

So a collection of collaborates is likewise a role (if they follow the rules over, that is)

A Function Can be in Pieces

We can produce features that behave differently relying on the input value

Example: A feature through 2 pieces:

as soon as x is less than 0, it gives 5, as soon as x is 0 or more it provides x2
Here are some instance values: x y
-1 5
0 0
2 4
4 16
... ...

Read more at Piecewise Functions.

Explicit vs Implicit

One last topic: the terms "explicit" and also "implicit".

Explicit is as soon as the attribute mirrors us how to go straight from x to y, such as:

y = x3 − 3

When we know x, we have the right to find y

That is the timeless y = f(x) stylethat we regularly work-related through.

Implicit is when it is not given directly such as:

x2 − 3xy + y3 = 0

When we recognize x, exactly how perform we uncover y?

It might be difficult (or impossible!) to go directly from x to y.

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"Implicit" originates from "implied", in various other words presented indirectly.



a duty relates inputs to outputs a role takes aspects from a set (the domain) and relates them to aspects in a collection (the codomain). all the outputs (the actual worths connected to) are together referred to as the rangea duty is a special kind of relation where: eextremely element in the doprimary is had, and also any type of input produces only one output (not this or that) an input and its matching output are together referred to as an ordered pairso a function deserve to likewise be seen as a collection of ordered pairs
Injective, Surjective and Bijective Domajor, Range and Codomain Summary to Sets Sets Index