In the new pattern of all Bschool entrance exams, different exam boards giving an importance in this area. An average of 4 to 5 questions in almost all the top level exams (CAT,XAT etc)can expect from this chapter. XAT contains a large number of questions related to the user defined functions than the pure mathematical functions. A clear theoretical awareness of the concept of functions is required to solve most of the questions.
 Basic concepts of sets and relations
 Definition of functions
 Domain, co domain and range of a function
 Understanding functions
 Value of a function
 Operations in functions
 Classifying functions
 Graphical representation
 Maxima and minima in quadratic function
Basic concepts and Terminologies
Cross product or Cartesian product of two sets
Let us consider two non empty sets A and B. A= {a, b, c} and B= {1, 2}
Cross product of set A and B means set of all different possible mappings from set A to B. Set of all possible mappings can arrange as set of ordered pairs and this set of all relations can be expressed as A*B(read as A cross B)
A*B={(a,1), (a,2) , (b,1) , (b,2) , (c,1) , (c,2)}
Number of elements in A*B is the product of number of elements from set A and number of elements from set B.
A*B is also called the Cartesian product of the sets A and B.
Definition:
If A and B are two nonempty sets, then the Cartesian product of A and B is,
A*B = {(x , y) : x ε A and y ε B }
Either A or B is an empty set the A*B is also an empty set.
If (x, y) = (a, b) then x=a and y = b
Relation
A relation from set A to set B is the subset of Cartesian product A*B. Each of the selected ordered pairs from A * B describes a relation between the first element and the second element.
Domain, Co domain and Range of a relation
In a relation defined from set A to set B, the set of all first elements of the ordered pairs is called the domain of the relation and the set of all second elements (images) in the ordered pair is called the range of the relation. Set B is called the codomain of the relation
i.e. Range ⊆ codomain
Example
Let A= {1, 2, 3, 4} B= {1, 2, 3, 4, 5} and R is a relation defined from set A to set B
R= {(x, y): y = x+2, x ε A and y ε B}
Then R= {(1, 3), (2, 4), (3, 5)}
Domain of R = {1, 2, 3}
Range of R = {3, 4, 5}
Codomain of R = {1, 2, 3, 4, 5}
Functions:
Functions are basically relations between two sets A and B.
When considering a relation from set A to set B, if each element in set A has one and only one image in set B, then the relation is called a function. 
Let f is a function from set A to B then f(a) = b , where a ε A and b ε B and b is called image of a.
Illustrated examples:
A= {1, 2, 3, 4} and B= {a, b, c, d}
 f_{1} = {(1,a),(2,a),(3,a),(4,a)} is a function. i.e. each element in set A has one and only one image in set B.
Domain of f_{1} = {1, 2, 3, 4}
Range of f_{1} = {a}
 f_{2}={(1,a),(2,b),(3,c),(4,d)} is a function.
Domain of f_{2} = {1, 2, 3, 4}
Range of f_{2} = {a, b, c, d}
 f_{3} = {(1, a), (2, b), (3, c} is not a function because the element 1 and 2 from set A does not have any image in set B.
 f_{4} = {(1, a),(1,b), (2, b),(2,b),(3,a), (4, d} is not a function because the element 4 in set A have more than one image in set B.
Value of a function:
Value of a function at certain input means the value of f(x) at certain value of x.
e.g. Let f(x) = 2x^{2} + 1
Then f (1) = 2(1)^{2} + 1 = 3
f (2) = 2(2)^{2} + 1 = 5
f (n+1) = 2(n+1)^{2} + 1
= 2(n^{2}+2n+1) + 1
= 2n^{2}+4n+2+1
= 2n^{2}+4n+3
Operations on functions:
Functions are following the basic mathematical operations such as addition, subtraction, multiplication, division etc.
Let f(x) and g(x) are two different functions in x
(f + g)(x) = f(x) + g(x)
(f  g)(x) = f(x)  g(x)
(f * g)(x) = f(x) * g(x)
(f/g)(x) = f(x)/g(x) where g(x) ≠ 0
Illustrated examples
If f(x) = 2x and g(x) = x + 1 then
 (f + g)(x) = f (x) + g (x)
= 2x + x + 1
= 3x + 1
 (fg)(x) = f(x)  g(x)
= 2x  (x+1)
= x1
 (f * g)(x) = f(x) * g(x)
= 2x(x+1)
= 2x^{2}+2x
 (f/g)(x) = f(x)/g(X) = 2x/x+1
Real Function:
Let f be a function from set A to set B. If A and B are the subset of the set of real numbers then f is a real function.
In this topic we are dealing only with real functions.
Classification of functions and corresponding graphical representation
Functions can be mainly classified into two
 Algebraic functions
 Transcendental functions
Algebraic functions
A function that can be expressed in algebraic forms is called an algebraic function.
E.g.: 4x+3, x^{2}  2/x^{2} + 4 , 5x^{2}  7x+1
Algebraic functions mainly classified into the following functions
 Polynomial function
A function f(x) can be expressed as polynomial function if and only if f can b expressed in the form
f(x) = a_{0 }+ a_{1}x + a_{2}x^{2 }+.... + a_{n}x^{n} , where n is a whole number and a_{1}, a_{2},... a_{n} are real numbers
E.g. f(x) = 3x^{4}+4x^{3}2x+1
g(x) = √3 x^{2} x + √2
Both the domain and range of a polynomial function is the set of all real numbers(R)
2. Identity function
If a function in the form f(x) = x, that is the input itself is the output, then it is called an Identity function
Both the domain and range of the identity function is the set of all real numbers.
3. Constant function
If all the input of a function have a common output i.e. f(x) = c, where c is a constant then the function is constant.
Domain = R Range = {c}
E.g. Equations for X and Y axis are the good examples for constant function
Y= 0 in the linear equation for representing X axis. i.e. for any value of x there should be one and only one value for y i.e. y = 0
E.g. f(x) = 3
i.e. y = f(x) = 3
X  4  3  2  1  0  1  >2 
y  3  3  3  3  3  3  3 
4. Rational functions:
Functions of the form f(x)/g(x) is called a rational function, where f(x) and g(x) are polynomial functions and g(x) ≠ 0
E.g. f(x) = 1/x
Domain = R  {0}
Range = R  {0}
5. Irrational functions:
If an algebraic function containing any irrational terms then the function is irrational.
E.g. y = √x
Here x ≥ 0 Domain = [0, ∞)
y = √x ≥ 0 Range = [0, ∞)
6. Linear Functions:
A function in the form f(x) = ax + b, where a and b are any two real numbers and a≠ 0 is called a linear function.
Graph of any linear function is a straight line. Both the domain and range of a linear function is the set of all real numbers.
E.g. f(x) = 2x+1
Domain = R
Range = R
y= f(x) = 2x+1
X  2  1  0  1  2 
y  3  1  1  3  5 
7.Quadratic Function:
A function of the form f(x) = ax^{2}+bx+c, where a, b and c are constants (Real numbers) and a≠ 0 is called a quadratic function.
Graph of a quadratic function is a parabola.
E.g. f(x) = x^{2}
i.e. y = x^{2}
X  3  2  1  0  1  2  3 
y  9  4  1  0  1  4  9 
 The lowest or highest point of the graph is called the vertex of the parabola
 Line of symmetry of the graph of a quadratic function with respect to x is y axis and this is simply called the axis of the parabola
Maximum and minimum value of a quadratic function
f(x) = ax^{2 }+ bx + c is the standard form of a quadratic function.
When a > 0, then the parabola open upward. Then the function will have a minimum value.
When a < 0, then the parabola open downward. Then the function will have a maximum value.
Vertex of the parabola is [b/2a,f(b/2a)] or [b/2a, (4ac b^{2})/4a]
The maximum or minimum value of the quadratic function = 4ac b^{2}/4a This is occurred when x = When a < 0, function has a maximum value.

E.g. Find the vertex of the parabola y = 2x^{2 }+ 3x + 4
a = (coefficient of x^{2 }) = 2
b = (coefficient of x) = 3
c = (constant term) = 4
x coordinates of vertex = b/2a = 3/4
y coordinates of vertex = (4ac b^{2})/4a
=(4*2*4)3^{2}/ 4 * 2
=329/8
=23/8
Vertex of the parabola = ((3/4) , (23/8))
E.g. Find the maximum and minimum value of the function f(x) = x^{2 }+2x  1
Solution:
Coefficient of x^{2 }= 1. This is positive
the maximum value is
Hence we can find the minimum value.
Minimum value of the function = 4ac b^{2}/4a
=(4*1*(1)) 2^{2}/4*1
= 44/4*1
=8/4 = 2
8. Modulus function (Absolute value function)
A function f of the form f(x) = for each x ε R is called a modulus function.
If 'x' is a non negative real number, then f(x) = x
If 'x' is a negative number then f(x) = x
i.e.4 = 4
4 = (4) = 4
Domain of the modulus function is the set of all real numbers but the range is the set of all non negative real numbers.
i.e. Domain = R
Range = R^{+} or [0,∞)
Graph of f(x) =
x  2  1  0  1  2 
Y= x  2  1  0  1  2 
9. Greatest integer function
A greatest integer function f(x) = [x] is defined as the value of the greatest integer, less than or equal to x
E.g. [3.2] =3
[5.9] = 5
[7.2] = 8
Domain =R (Real numbers)
Range = Z (set of integers)
10. Smallest integer function
Smallest integer function f(x) = {x} is defined as the value of smallest integer greater than or equal to x.
E.g. {3.1} = 4
{7.4}= 7
Domain = R
Range = Z
11. Odd Function
If f (x) =  f(x) then f is an odd function
E.g. If f(x) = x + 2x^{3}
Then
i.e. f(2) = f(2)
f is an odd function
12. Even Function
If f(x) = f(x) then f is an even function
E.g. If f(x) = 2x^{2}+1
f (1) = 2(1)^{2}+1 = 3
and f(1) = 2(1)^{2}+1 = 3
i.e. f(1) = f(1)
f is an even function
Transcendental functions
A function which cannot be expressed algebraically is called a transcendental function.
Main transcendental functions are explained below.
 Trigonometric function
A function defined in the form of a trigonometric ratio is called a trigonometric function
E.g. f(x) = Sin x
g(x) = Cos x
etc
E.g. f(x)= Sin x
Sin x is a periodic function with period 2π.
Domain =R
Range = [1,1]
 Logarithmic function
A function of the form f(x) = log x is called a logarithmic function
E.g f(x) = log_{e}x
Domain = R+
Range = R
Main Objectives under this module:
 More understanding of the graphs
 Transformations of a graph
 Vertical shift
 Horizontal shift
 Stretch and Shrink
 Changing directions
 Maximum and Minimum value of a function
 Application of derivatives in Maxima and Minima
More understanding on the graph of a function.
Transformations of a graph
 Vertical shift:
Through the sufficient changes in the function, its corresponding graph can move upward or downward.
Consider the graph of the function f(x) = x^{2}.
 f(x) → f(x) + k, where 'k' is a positive real constant.
Then the graph moves 'k' units upward.
 f(x) → f(x)  k, where 'k' is a positive real constant.
Then the graph moves 'k' units downward.
 Horizontal shift:
 f(x) → f(x  k), where 'k' is a positive real constant.
Then the graph moves 'k' units towards right.
 f(x) → f(x + k), where 'k' is a positive real constant.
Then the graph moves 'k' units towards left.
 Shrink and stretch:
 f(x) → k f(x), where k > 1
Then the graph will shrink 'k' times along y axis
 f(x) → 1/k * f(x), where k > 1
Then the graph will stretch 'k' units along y axis.
 Changing direction:
f(x) →  f(x)
Then the graph will revolve 180° about x axis.
Maxima and Minima
Here we are discussing the maximum and minimum value of a function. Its conventional application is lying in the area of differential calculus, even though we can think about some of the simple methods irrespective of the application of differentiation for finding the maxima and minima.
Examples:
 What is the minimum value of the function x^{2} + 6x + 12 ?
Solution:
x^{2} + 6x + 12 = x^{2} + 6x + 9 + 3
= (x + 3)^{2} + 3
Now the minimum value for (x +3)^{2} can be equal to zero, when x = 3.
Hence the minimum value of the function is 0 + 3 = 3.
Alternate method 1: (Formula)
Apply the formula 4ac b^{2}/4a for finding the minimum value of the given function.
a = 1
b = 6
c = 12
Minimum value = (4*1*12  6^{2})/4*1 = 3
Alternate method 2: (differentiation)
Let y = x^{2} + 6x + 12
y' = dy/dx = 2x + 6
y'' = d^{2}y/dx^{2} = 2
y'' > 0, hence the function has a minimum value.
Equate y' to zero to get the value of 'x' at which the given function has a minimum value.
2x + 6 = 0
x = 3
y = (3)^{2} + 6(3) + 12 = 3
Hence the minimum value of y = 3
 What are the maximum and minimum values of the function y = x^{2}+ 2x+1/x^{2}+ x+1
Solution:
Method 1:
y = x^{2}+ 2x+1/x^{2}+ x + 1
y (x^{2} x+1) = x^{2}+ 2x+1
(y  1) + (y  2) x + (y  1) = 0
As 'x' is a real number, b^{2} 4ac ≥ 0
(y  2)^{2}  4 (y 1) ^{2} ≥ 0
y (3y  4) ≤ 0
y ≥ 0 and 3y  4 ≤ 0
y ≥ 0 and y ≤ 4/3
Hence the minimum value of the function is '0' and the maximum value of the function is 4/3.
Method 2:
Application of derivatives:
Quotient rule of differentiation: d[U/V]/dx = (U'VUV')/V^{2} 
Equate the derivative of the function to zero to get the values at which function has the minimum and maximum values.
d[(x^{2}+ 2x + 1)/(x^{2}+ x+1)]/dx = (2x+2)(x^{2} + x + 1)  (x^{2} + 2x + 1)(2x+1)/(x^{2}+x+1)2 = 0
x^{2}1 = 0
x = ± 1
When x = 1 → y = 0
When x = 1 → y = 4/3
The minimum value of the function is 0.
The maximum value of the function is 4/3.