# Concept of Relation

#### Topics

• ##### Angle and Its Measurement
• Directed Angle
• Angles of Different Measurements
• Angles in Standard Position
• Measures of Angles
• Area of a Sector of a Circle
• Length of an Arc of a Circle
• ##### Trigonometry - 1
• Introduction of Trigonometry
• Trigonometric Functions with the Help of a Circle
• Signs of Trigonometric Functions in Different Quadrants
• Range of Cosθ and Sinθ
• Trigonometric Functions of Specific Angles
• Trigonometric Functions of Negative Angles
• Fundamental Identities
• Periodicity of Trigonometric Functions
• Domain and Range of Trigonometric Functions
• Graphs of Trigonometric Functions
• Polar Co-ordinate System
• ##### Trigonometry - 2
• Trigonometric Functions of Sum and Difference of Angles
• Trigonometric Functions of Allied Angels
• Trigonometric Functions of Multiple Angles
• Trigonometric Functions of Double Angles
• Trigonometric Functions of Triple Angle
• Factorization Formulae
• Formulae for Conversion of Sum Or Difference into Product
• Formulae for Conversion of Product in to Sum Or Difference
• Trigonometric Functions of Angles of a Triangle
• ##### Straight Line
• Locus of a Points in a Co-ordinate Plane
• Straight Lines
• Equations of Line in Different Forms
• General Form of Equation of a Line
• Family of Lines
• ##### Conic Sections
• Double Cone
• Conic Sections
• Parabola
• Ellipse
• Hyperbola
• ##### Measures of Dispersion
• Meaning and Definition of Dispersion
• Measures of Dispersion
• Range of Data
• Variance
• Standard Deviation
• Change of Origin and Scale of Variance and Standard Deviation
• Standard Deviation for Combined Data
• Coefficient of Variation
• ##### Permutations and Combination
• Fundamental Principles of Counting
• Invariance Principle
• Factorial Notation
• Permutations
• Permutations When All Objects Are Distinct
• Permutations When Repetitions Are Allowed
• Permutations When Some Objects Are Identical
• Circular Permutations
• Properties of Permutations
• Combination
• Properties of Combinations
• ##### Methods of Induction and Binomial Theorem
• Principle of Mathematical Induction
• Binomial Theorem for Positive Integral Index
• General Term in Expansion of (a + b)n
• Middle term(s) in the expansion of (a + b)n
• Binomial Theorem for Negative Index Or Fraction
• Binomial Coefficients
• ##### Limits
• Concept of Limits
• Factorization Method
• Rationalization Method
• Limits of Trigonometric Functions
• Substitution Method
• Limits of Exponential and Logarithmic Functions
• Limit at Infinity
• ##### Continuity
• Continuous and Discontinuous Functions
• ##### Differentiation
• Definition of Derivative and Differentiability
• Rules of Differentiation (Without Proof)
• Derivative of Algebraic Functions
• Derivatives of Trigonometric Functions
• Derivative of Logarithmic Functions
• Derivatives of Exponential Functions
• L' Hospital'S Theorem
• Definition of Relation
• Domain
• Co-domain and Range of a Relation

## Definition

A relation R from a non-empty set A to a non-empty set B is a subset of the cartesian product  A × B. The subset is derived by describing a relationship between the first element and the second element of the ordered pairs in A × B. The second element is called the image of  the first element.

The set of all first elements of the ordered pairs in a relation R from a set A to a set B is called the domain of the relation R.

The set of all second elements in a relation R from a set A to a set B is called the range of the relation R. The whole set B is called the codomain of the relation R. Note that range ⊂ codomain.

## Notes

(i) A relation may be represented algebraically either by the Roster method or by the Set-builder method.
(ii) An arrow diagram is a visual representation of a relation.
Consider the two sets P = {a, b, c} and Q = {Ali, Bhanu, Binoy, Chandra, Divya}.

The cartesian product of P and Q has 15 ordered pairs which can be listed as P × Q = {(a, Ali), (a,Bhanu), (a, Binoy), ..., (c, Divya)}. We can now obtain a subset of P × Q by introducing a relation R between the first element x and the second element y of each ordered pair (x, y) as R= { (x,y): x is the first letter of the name y, x ∈ P, y ∈ Q}. Then R = {(a, Ali), (b, Bhanu), (b, Binoy), (c, Chandra)} A visual representation of this relation R (called an arrow diagram) is shown in Fig .
A relation R from A to A is also stated as a relation on A.

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