# Principle of Mathematical Induction

#### 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

## Notes

(i) The statement is true for n = 1, i.e., P(1) is true, and
(ii) If the statement is true for n = k (where k is some positive integer), then the statement is also true for n = k + 1, i.e., truth of P(k) implies the truth of P (k + 1).
Then, P(n) is true for all natural numbers n.
Property (i) is simply  a statement of fact. There may be situations when a statement is true for all n ≥ 4. In this case, step 1 will start from n = 4 and we shall verify the result for n = 4, i.e., P(4). Suppose there is a given statement P(n)  involving the natural number n such that

Property (ii) is a conditional property. It does not assert that the given statement is true for n = k, but only that if it is true for n = k, then it is also true for n = k +1. So, to prove that the  property holds , only prove that conditional proposition:
If the statement is true for n = k, then it is also true for n = k + 1.
This is sometimes referred to as the inductive step. The assumption that the given statement is true for n = k in this inductive step is called the inductive hypothesis.
For example, frequently in mathematics, a formula will be discovered that appears to fit a pattern like
1 = 1^2 =1
4 = 2^2 = 1 + 3
9 = 3^2 = 1 + 3 + 5
16 = 4^2 = 1 + 3 + 5 + 7, etc.
It is worth to be noted that the sum of the first two odd natural numbers is the square of second natural number, sum of the first three odd natural numbers is the square of third natural number and so on.Thus, from this pattern it appears that
1 + 3 + 5 + 7 + ... + (2"n" – 1) = "n"^2, i.e,
the sum of the first n odd natural numbers is the square of n.
Let us write
"P"("n"): 1 + 3 + 5 + 7 + ... + (2"n" – 1) = "n"^2.  We wish to prove that P(n) is true for all n.
The first step in a proof that uses mathematical induction is to prove that P (1) is true. This step is called the basic step. Obviously
1 = 1^2, i.e., P(1) is true.
The next step is called the inductive step. Here, we suppose that P (k) is true for some positive integer k and we need to prove that P (k + 1) is true. Since P (k) is true, we have
1 + 3 + 5 + 7 + ... + (2k – 1) = k^2 ... (1)
Consider
1 + 3 + 5 + 7 + ... + (2k – 1) + {2(k +1) – 1} ... (2)
= k^2 + (2k + 1) = (k + 1)^2 [Using (1)]
Therefore, P (k + 1) is true and the inductive proof is now completed. Hence P(n) is true for all natural numbers n.

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