Types of Functions
The types of functions are defined on the basis of domain, range, and function expression. The expression used to write the function is the prime defining factor for a function. And the relationship between the elements of the domain set and the range set also accounts for the type of function. The classification of functions helps to easily understand and learn the different types of functions.
Every mathematical expression which has an input value and a resulting answer can be conveniently presented as a function. Here we shall learn about the types of functions and their definition, examples.
What are the Different Types of Functions?
The function y = f(x) is classified into different types of functions, based on factors such as the domain and range of a function, and the function expression. The functions have a domain x value which is the input. The domain value can be a number, angle, decimal, fraction. And the range is the y value or the f(x) value which is generally a numeric value. The types of functions have been classified into the following four types.
 Based on the Set Elements
 Based on Equation
 Based on Range
 Based on Domain
Representation of Functions
There are three different forms of representation of functions. The functions need to be represented to showcase the domain values and the range values and the relationship between them. The functions can be represented with the help of Venn diagrams, graphical formats, and roster form. The details of each of the forms of representation are as follows.
Venn Diagram: The Venn diagram is an important format for representing the function. The Venn diagrams are usually presented as two circles with arrows connecting the element in each of the circles. The domain is presented in one circle and the range values are presented in another circle. And the function defines the arrows, and how the arrows connect the different elements in the two circles.
Graphical Form: Functions are easy to understand if they are represented in the graphical form with the help of the coordinate axes. Representing the function in graphical form, helps us to understand the changing behavior of the functions if the function is increasing or decreasing. The domain of the function  the x value is represented along the xaxis, and the range or the f(x) value of the function is plotted with respect to the yaxis.
Roster Form: The domain and range of the function are represented in flower brackets with the first element of a pair representing the domain and the second element representing the range. Let us try to understand this with the help of a simple example. For a function of the form f(x) = x^{2}, the function is represented as {(1, 1), (2, 4), (3, 9), (4, 16)}. Here the first element is the domain or the x value and the second element is the range or the f(x) value of the function.
Classification of Types of Functions
The types of functions are classified further to help for easy understanding and learning. The types of functions have been further classified into four different types, and are presented as follows.
Based on Elements 

Based on Equation 

Based on the Range 

Based on the Domain 

Types of Functions  Based on Set Elements
These types of functions are classified based on the number of the relationship between the elements in the domain and the codomain. The different types of functions based on set elements are as follows.
One One Function
A onetoone function is defined by f: A → B such that every element of set A is connected to a distinct element in set B. The onetoone function is also called an injective function. Here every element of the domain has a distinct image or codomain element for the given function.
Many to One Function
A many to one function is defined by the function f: A → B, such that more than one element of the set A are connected to the same element in the set B. In a many to one function, more than one element has the same codomain or image. If a many to one function, in the codomain, is a single value or the domain element are all connected to a single element, then it is called a constant function.
Onto Function
In an onto function every codomain element is related to the domain element. For a function defined by f: A → B, such that every element in set B has a preimage in set A. The onto function is also called a subjective function.
One One and Onto Function (Bijection)
A function that is both a one one and onto function is called a bijective function. Here every element of the domain is connected to a distinct element in the codomain and every element of the codomain has a preimage. Also in other words every element of set A is connected to a distinct element in set B, and there is not a single element in set B which has been left out.
Into Function
The into function is exactly opposite in properties to an onto function. Here there are certain elements in the codomain that do not have any preimage. The elements in the set B are excess and are not connected to any elements in the set A.
Constant Function
A constant function is an important form of a many to one function. In a constant function, all the domain elements have a single image. The constant function is of the form f(x) = K, where K is a real number. For the different values of the domain(x value), the same range value of K obtained for a constant function.
Types of Function  Based on Equation
The algebraic expressions are also functions and are based on the degree of the polynomial. The functions based on equations are classified into the following equations based on the degree of the variable 'x'.
 The polynomial function of degree zero is called a Constant Function.
 The polynomial function of degree one is called a Linear Function.
 The polynomial function of degree two is called a Quadratic Function.
 The polynomial function of degree three is a Cubic Function.
Let us understand about each of these functions in detail.
Identity Function
The identity function has the same domain and range. The identity function equation is f(x) = x, or y = x. The domain and range of the identity function is of the form {(1, 1), (2, 2), (3, 3), (4, 4).....(n, n)}.
The graph of the identity function is a straight line that is equally inclined to the coordinate axes and is passing through the origin. The identity function can take both positive and negative values and hence it is present in the first and the third quadrants of the coordinate axis.
Linear Function
A polynomial function having the firstdegree equation is a linear function. The domain and range of a linear function is a real number, and it has a straight line graph. Equations such as y = x + 2, y = 3x, y = 2x  1, are all examples of linear functions. The identity function of y = x can also be considered a linear function.
The general form of a linear function is f(x) = ax + b, where a, b are real numbers. Graphically to represent the linear function can be represented by the equation of a line y = mx + c, where m is the slope of the line and c is the yintercept of the line.
Quadratic Function
A quadratic function has a seconddegree quadratic equation and it has a graph in the form of a curve. The general form the the quadratic function is f(x) = ax^{2} + bx + c, where a ≠ 0 and a, b, c are constant & x is a variable. The domain and range of the quadratic function is R.
The graph of a quadratic equation is a nonlinear graph and is parabolic in shape. Examples of quadratic functions are f(x) = 3x^{2} + 5, f(x) = x^{2}  3x + 2.
Cubic Function
A cubic function has an equation of degree three. The general form of a cubic function is f(x) = ax^{3} + bx^{2} + cx +d, where a ≠ 0 and a, b, c, and d are real numbers & x is a variable. The domain and range of a cubic function is R.
The graph of a cubic function is more curved than the quadratic function. An example of cubic function is f(x) = 8x^{3} + 5x^{2} + 3.
Polynomial Function
The general form of a polynomial function is f(x) = a^{n}x^{n} + a^{n1}x^{n1} + a^{n2}x^{n2}+ ..... ax + b. Here n is a nonnegative integer and x is a variable. The domain and range of a polynomial function are R. Based on the power of the polynomial function, the functions can be classified as a quadratic function, cubic function, etc.
Types of Functions  Based on Range
Here the types of functions have been classified based on the range which is obtained from the given functions. The different types of functions based on the range are as follows.
Modulus Function
The modulus function gives the absolute value of the function, irrespective of the sign of the input domain value. The modulus function is represented as f(x) = x. The input value of 'x' can be a positive or a negative expression. The graph of a modulus function lies in the first and the second quadrants since the coordinates of the points on the graph are of the form (x, y), (x, y).
Rational Function
A function that is composed of two functions and expressed in the form of a fraction is a rational function. A rational fraction is of the form f(x)/g(x), and g(x) ≠ 0. The functions used in this rational function can be a algebraic function, or any other function. The graphical representation of these rational functions is similar to the asymptotes since it does not touch the axis lines.
Signum Function
The signum function helps us to know the sign of the function and does not give the numeric value or any other values for the range. The range of the signum function is limited to {1, 0, 1}. For positive value of the domain the signum function gives an answer of 1, for negative values the signum function gives an answer of 1, and for 0 value of domain, the image is 0. The signum function has wide application in software programming.
Even and Odd Function
The even and odd functions are based on the relationship between the input and the output values of the function. For the negative domain value, if the range is also a negative value of the range of the original function, then the function is an odd function. And for the negative domain value, if the range is the same as that oif the original function, then the function is an even function.
If f(x) = f(x), for all values of x, then the function is an even function, and if f(x) = f(x), for all values of x, then the function is an odd function. An example of even functions are x^{2}, Cosx, Secx, and an example of odd functions are x^{3}, Sinx, Tanx.
Periodic Function
The function is considered a periodic function if the same range appears for different domain values and in a sequential manner. The trigonometric functions can be considered periodic functions. For example, the function f(x) = Sinx, have a range equal to the range of [1, 1] for the different domain values of x = nπ + (1)^{n}x. Similarly, we can write the domain and the range of the trigonometric functions and prove that the range shows up in a periodic manner.
Inverse function
The inverse of a function f(x) is denoted by f^{1}(x). For inverse of a function the domain and range of the given function is reverted as the range and domain of the inverse function. The inverse of a function can be prominently seen in algebraic functions and in inverse trigonometric functions. The domain of Sinx is R and its range is [1, 1], and for Sin^{1}x the domain is [1, 1] and the range if R. The inverse of a function exists, if it is a bijective function.
If a function f(x) = x^{2}, then the inverse of the function is f^{1}(x) = \(\sqrt x\).
Greatest Integer Function
The greatest integer function is also known as the step function. The greatest integer function rounds up the number to the nearest integer less than or equal to the given number. Clearly, the input variable x can take on any real value. However, the output will always be an integer. Also, all integers will occur in the output set. Thus, the domain of this function is real numbers R, while its range will be integers (Z).
The greatest integer function graph is known as the step curve because of the step structure of the curve.The greatest integral function is denoted as f(x) = ⌊x⌋. For a function taking values from [1, 2), the value of f(x) is 1.
Composite Function
The composite functions are of the form of gof(x), fog(x), h(g(f(x))), and is made from the individual functions of f(x), g(x), h(x). The composite functions made of two functions have the range of one function forming the domain for another function. Let us consider a composite function fog(x), which is made up of two functions f(x) and g(x).
Here we write fog(x) = f(g(x)). The range of g(x) forms the domain for the function f(x). It can be considered as a sequence of two functions. If f(x) = 2x + 3 and g(x) = x + 1 we have fog(x) = f(g(x)) = f(x + 1) = 2(x + 1) + 3 = 2x + 5.
Types oF Functions  Based on Domain
Functions are used in all the other topics of maths. The functions have been classified based on the types of equations used to define the functions. The function equations general have algebraic expressions, trigonometric functions, logarithms, exponents, and hence are named based on these domain values. The three broad type of functions based on domain value are as follows.
Algebraic Function:
An algebraic function is helpful to define the various operations of algebra. The algebraic function has variable, coefficient, constant term and the various arithmetic operators such as addition, subtraction, multiplication, division. An algebraic function is generally of the form of f(x) = a^{n}x^{n} + a^{n  1}x^{n  1}+ a^{n2}x^{n2}+ ....... ax + c.
The algebraic function can also be represented graphically. The algebraic function is also termed as linear function, quadratic function, cubic function, polynomial function, based on the degree of the algebraic equation.
Trigonometric Functions
The trigonometric functions also have a domain and range similar to any other functions. The six trigonometric functions are f(θ) = sinθ, f(θ) = cosθ, f(θ) = tanθ, f(θ) = secθ, f(θ) = cosecθ. Here the domain value θ is the angle and is in degrees or in radians.These trigonometric functions have been taken based on the ratio of the sides of a rightangle triangle, and are based on the Pythagoras theorem.
Further from these trigonometric functions, inverse trigonometric functions have also been derived. The domain of the inverse trigonometric function is a real number value and its range is an angle. The trigonometric functions and the inverse trigonometric functions are also sometimes referred to as periodic functions since the principal values are repeated.
Logarithmic Functions
Logarithmic functions have been derived from the exponential functions. The logarithmic functions are considered as the inverse of exponential functions. Logarithmic functions have a 'log' in the function and it has a base. The logarithmic function is of the form y = \(\log_ax \). Here the domain value is the input value of 'x' and is calculated using the napier logarithmic table. The logarithic function gives the number of exponential times to which the base has raised to obtain the value of x. The same logarithmic function can be expressed as a exponential function as x = a^{y}.
Related Topic
The following topic help in a better understanding of the types of functions.
Solved Examples on Types of Functions

Example 1: For the given functions f(x) = 3x + 2 and g(x) = 2x  1, find the value of fog(x).
Solution:
The given two functions are f(x) = 3x + 2 and g(x) = 2x  1.
We need to find the function fog(x).
fog(x) = f(g(x))
= f(2x1)
= 3(2x  1) + 2
= 6x  3 + 2
= 6x  1
Answer: Therefore fog(x) = 6x  1

Example 2: Find the inverse function of the function f(x) = 5x + 4.
Solution:
The given function is f(x) = 5x + 4
we rewrite it as y = 5x + 4 and simplify it to find the value of x.
y = 5x + 4
y  4 = 5x
x = (y  4)/5
f^{1}(x) = (x  4)/5
Answer: Therefore the inverse function is f^{1}(x) = (x  4)/5
FAQs on Types of Functions
What are the Various Forms of Representation of Functions?
The functions are generally represented in the form of an equation y = f(x), where x is the domain and y or f(x) is the range of the function. The functions with the domain and range elements are also represented as venn diagrams or as roster form. In roster form the domain and range of the function are represented as {\((x_1, f(x_1)), (x_2, f(x_2)), (x_3, f(x_3))\)}.
What are the Types of Functions?
The types of functions can be broadly classified into four types.
 Based on Element: One to one Function, many to one function, onto function, one to one and onto function, into function.
 Based on Domain: Algebraic Functions, Trigonometry functions, logarithmic functions.
 Based on Range: Modulus function, rational function, signum function, even and odd function, greatest integer function.
 Based on Equations: Identity function, linear function, quadratic function, cubic function, polynomial function.
How do you Determine the Types of Functions?
The types of functions can be determined based on the domain, range, and functional equation. Further classifying functions into types of functions helps to group and easily understand each of the types of functions. All the trigonometric functions can be grouped under periodic functions. Functions such as identity function, linear function, the quadratic, cubic function can put under polynomial functions. Thus the function equation y = f(x) is helpful to find define the type of function.
What Type of Functions is Always Continuous?
The functions which have a range for every input value of the domain can be termed as a continuous function. The simplest example of a continuous function is the identity function which has equal domain and range value. Other examples of continuous functions are the trigonometric sine function and cosine functions.
What are the other math applications of Types of Functions?
The types of functions have enormous applications in algebra, trigonometry, logarithms, exponents. All the algebraic expressions can be counted as functions as it has an input domain value of x and the output range, which is the answer of the algebraic function. The trigonometric functions also have the angle value as the domain and range value.
Can any Math Equation be Considered a Function?
Yes. A math equation that is not equal to zero can be considered as a function. Alternatively, a math equation with two variables where one variable can be taken as a domain and the other variable can be taken as the range, can be called a function.
What are the applications of types of functions?
The types of functions has numerous applications in physics, engineering, computer sciences, artificial intelligence. All of these fields aim at connecting one set of data points (domain) to another set of data points(range). Also, the functions help in representing the huge set of data points in a simple mathematical expression of the formal y = f(x).