Functions are a mathematical relationship. They involve an input and produce an output. Using Algebra, functions can be written as f and the input as x, creating f(x). Functions can be complex and use different Algebra, for example, 
or
. There are two different types of functions, composite and inverse.
Composite functions
A composite function involves combining two or more functions to create a new function. This is also known as a function of a function. For example, let's look at fg(x). This means that you first find g(x), then you use the output of that to solve f(x).
Given that f(x) = x + 2 and g(x) = 3x − 1 find fg(4)
First, you need to solve g(4)
g(4) = 3(4) − 1
g(4) = 11
Now you can put the output of g(4), which was 11, into your f function to find fg(4)
f(11) = 11 + 2
f(11) = 13
Therefore fg(4) = 13
It is important to solve the functions in a specific order as fg(x) is not the same as gf(x). Let's have a look at solving gf(4) to see how the answer is different:
Given that f(x) = x + 2 and g(x) = 3x − 1 find gf (4)
This time you need to solve f(4) first
f(4) = 4 + 2
f(4) = 6
Now you can use that output to find g(x) using 6
g(6) = 3(6) -1
g(6) = 17
Therefore gf(4) = 17. Remember, solve the function that is closest to the brackets first.
Consider f(x) = 2x + 4
Let f(x) = 2x + 4 = y
y = 2x + 4
This is the inverse of f(x).
What are mappings?
Mapping can take an input from a set of numbers and transform it into an output. A mapping can be considered as a function if an input creates a distinct output. Below are the four ways that we can map inputs and outputs:
Mapping inputs and outputs
Only two of these mappings create functions; they are one to one and many to one. The terms domain and range can be used when discussing input and output:
How are graphs used for functions?
Graphs are able to give you a visual representation of a function, each function will give you a different type of graph. There are many different Factors that will change the way the graph looks, such as;
Polynomial graphs
Polynomials can be described as expressions that may contain variables that are raised to a positive power, which may also be multiplied by a coefficient. Polynomials can seem complicated but they can also look very simple, for example, is a polynomial but so is. These expressions are also graphed to give you a visual representation and just like Graphs of functions they can look very different depending on the polynomial that is being graphed.
What are inequalities?
Inequalities are algebraic expressions that show how one term is less than, greater than or equal to another term. The symbols used to represent this are;
This shows you that 2x is greater than 4
This shows you that x is less than 10
This shows you that + 5 is greater than or equal to 20
Functions - Key takeaways
Functions have an input that affects the output.
Functions can be written using algebra.
There are two different types of functions, composite and inverse.
Mapping is used to show the domain and range of a function.
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Explanations 
Exams 
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. The function takes the outputs and maps them back to the input, and this means that 
and
will reflect each other.
