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Principle Of Mathematical Induction

Class 11th Mathematics Bihar Board Solution
Exercise 4.1
  1. 1+3+3^2 +3^n-1 = (3^n - 1)/2 Prove the following using the principle of…
  2. 1^3 + 2^3 + 3^3 + l l +n^3 = (n (n+1)/2)^2 Prove the following using the…
  3. Prove the following using the principle of mathematical induction for all n ∈ N…
  4. 1.2.3+2.3.4 + l +n (n+1) (n+2) = n (n+1) (n+2) (n+3)/4 Prove the following using…
  5. 1.3+2.3^2 +3.3^3 + l +n.3^n = (2n-1) 3^n+1 +3/4 Prove the following using the…
  6. 1.2 + 2.3 + 3.4 + …+n.(n+1) = [n (n+1) (n+2)/3] Prove the following using the…
  7. 1.3 + 3.5 + 5.7 +…+(2n - 1)(2n + 1)= n (4n^2 + 6n-1)/3 Prove the following using…
  8. 1.2 + 2.2^2 + 3.2^3 + …+n.2n = (n - 1)2n + 1 + 2 Prove the following using the…
  9. 1/2 + 1/4 + 1/8 + l + 1/2^n = 1 - 1/2^n Prove the following using the principle…
  10. 1/2.5 + 1/5.8 + 1/8.11 + l . + 1/(3n-1) (3n+2) = n/(6n+4) Prove the following…
  11. 1/1.2.3 + 1/2.3.4 + 1/3.4.5 + l . + 1/n (n+1) (n+2) = n (n+3)/4 (n+1) (n+2)…
  12. a + ar + ar^2 + …+ arn-1 = a (r^n - 1)/r-1 Prove the following using the…
  13. (1 + 3/1) (1 + 5/4) (1 + 7/9) .. (1 + (2n+1)/n^2) = (n+1)^2 Prove the following…
  14. (1 + 1/1) (1 + 1/2) (1 + 1/3) .. (1 + 1/n) = (n+1) Prove the following using…
  15. 1^2 + 3^2 + 5^2 +…+(2n -1)^2 = n (2n-1) (2n+1)/3 Prove the following using the…
  16. 1/1.4 + 1/4.7 + 1/7.10 + l . + 1/(3n-2) (3n+1) = n/(3n+1) Prove the following…
  17. 1/3.5 + 1/5.7 + 1/7.9 + l + 1/(2n+1) (2n+3) = n/3 (2n+3) Prove the following…
  18. 1+2+3 + l .+n 1/8 (2n+1)^2 Prove the following using the principle of…
  19. n (n + 1) (n + 5) is a multiple of 3. Prove the following using the principle…
  20. 102n - 1 + 1 is divisible by 11. Prove the following using the principle of…
  21. x2n - y2n is divisible by x + y. Prove the following using the principle of…
  22. 32n + 2 - 8n - 9 is divisible by 8. Prove the following using the principle of…
  23. 41n - 14n is a multiple of 27. Prove the following using the principle of…
  24. (2n + 7) (n + 3)^2 . Prove the following using the principle of mathematical…

Exercise 4.1
Question 1.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as


Now for Proving a statement by mathematical Induction the steps involved are:
Step 1: Verify that P(1) is true.
Step 2: By taking P(k) as true prove that P(k + 1) is also true.

Step 1:

First, we check if it is true for n = 1,



∴ It is true for n = 1.

Hence, P(1) is true.
Step 2:

Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1

Therefore,

P(k + 1) = 1 + 3 + 32 .......+ 3[(k + 1) - 1]

P(k + 1) = 1 + 3 + 32 ......+ 3k


[From equation (1)]





Which is equal to the Right hand side for n = k + 1. We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 2.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1,








[As k + 2 = (k + 1) + 1]


Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 3.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



Steps for Proving a statement using Mathematical Induction are:
Step 1: Verify that P(1) is true.
Step 2: If P(k) is true then P(k + 1) is also true.

Step 1:

First, we check if it is true for n = 1,



∴ It is true for n = 1.

Step 2:

Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]







Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 4.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]






Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 5.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]









Which is equal to the Right-hand side for n = k + 1. We proved that P(k + 1) is true.


Hence by the principle of mathematical induction, it is true for all n ∈ N.


Question 6.

Prove the following using the principle of mathematical induction for all n ∈ N

1.2 + 2.3 + 3.4 + …+n.(n+1) =


Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]





Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 7.

Prove the following using the principle of mathematical induction for all n ∈ N

1.3 + 3.5 + 5.7 +…+(2n – 1)(2n + 1)=


Answer:

Let the given statement be P(n), as



Steps involved in Proving Mathematical Induction are:

Step 1: Verify that P(1) is true.

Step 2: If P(k) is true than P(k + 1) will also be true.

Step 1:


First, we check if it is true for n = 1,



∴ It is true for n = 1.

Step 2:

Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]









Which is equal to the Right-hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by the principle of mathematical induction, it is true for all n ∈ N.


Question 8.

Prove the following using the principle of mathematical induction for all n ∈ N

1.2 + 2.22 + 3.23 + …+n.2n = (n – 1)2n + 1 + 2


Answer:

Let the given statement be P(n), as

Steps involved in solving a statement by mathematical Induction are:

Step 1: Verify that P(1) is true.
Step 2: If P(1) is true then P(2) is also true.

Step 1:

First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]






Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 9.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]





Which is equal to the Right hand side for n = k + 1. We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 10.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1



[From equation (1)]









Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 11.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]









Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 12.

Prove the following using the principle of mathematical induction for all n ∈ N

a + ar + ar2 + …+ arn–1 =


Answer:


Let the given statement be P(n), as


First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]




Which is equal to the Right hand side for n = k + 1. We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 13.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:


Let the given statement be P(n), as


First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]







Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 14.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]





Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 15.

Prove the following using the principle of mathematical induction for all n ∈ N

12 + 32 + 52 +…+(2n –1)2 =


Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1,









Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 16.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1



[From equation (1)]









Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 17.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:

Let the given statement be P(n), as



First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Solving the left hand side with n = k + 1




[From equation (1)]









Which is equal to the Right hand side for n = k + 1.We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 18.

Prove the following using the principle of mathematical induction for all n ∈ N



Answer:


Let the given statement be P(n), as


First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


…………..(1)


We shall prove that P(k + 1)is true,


Adding (k + 1) to both sides








We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 19.

Prove the following using the principle of mathematical induction for all n ∈ N

n (n + 1) (n + 5) is a multiple of 3.


Answer:

Let the given statement be P(n), as

P(n):n(n + 1)(n + 5) is a multiple of 3.

For solving a statement P(n) by mathematical induction following steps are involved.

Step 1:
Verify that P(1) is true.

Step 2:
If P(k) is true then P(k + 1) is also true.

Step 1:

First, we check if it is true for n = 1,

P(1):1(2)(6) = 12 is a multiple of 3;

∴ It is true for n = 1.

Hence, P(1) is true.

Step 2:

Now we assume that it is true for some positive integer k, such that


P(k): k(k + 1)(k + 5) = 3 m where m ∈ N ..........eq(1)


We shall prove that P(k + 1)is true,


P(k + 1): (k + 1)(k + 2)(k + 5 + 1)


⇒ (k + 1)(k + 2)(k + 5) + (k + 1)(k + 2)


⇒ k(k + 1)(k + 5) + (2)(k + 1)(k + 5) + (k + 1)(k + 2)


[From eq(1) we know that, k(k + 1)(k + 5) = 3 m]


⇒ 3 m + (k + 1)[2 k + 10 + k + 2]


⇒ 3m + (k + 2)(3k + 12)


⇒ 3m + 3(k + 2)(k + 4)


⇒ 3[m + (k + 2)(k + 4)]


Hence, P(k + 1) is also divisible by 3.


We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.


Question 20.

Prove the following using the principle of mathematical induction for all n ∈ N

102n – 1 + 1 is divisible by 11.


Answer:


Let the given statement be P(n), as

is divisible by 11.


First, we check if it is true for n = 1,



∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


P(k):102k - 1 + 1 = 11m where m ∈ N


102k - 1 = 11m - 1 ………….(1)


We shall prove that P(k + 1)is true,


P(k + 1):102k + 1 + 1


⇒ 102k - 1.102 + 1


⇒ (11m - 1).100 + 1 From equation(1)


⇒ 1100m - 100 + 1


⇒ 1100m - 99


⇒ 11(100m - 9)


We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 21.

Prove the following using the principle of mathematical induction for all n ∈ N

x2n – y2n is divisible by x + y.


Answer:

Let the given statement be P(n), as


P(n): x2n – y2n is divisible by (x + y).


First, we check if it is true for n = 1,


P(1): x2 - y2 = (x - y)(x + y);


∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


P(k):x2k - y2k = m(x + y) where m ∈ N.


x2k = y2k + m(x + y) ………….(1)


We shall prove that P(k + 1) is true,


P(k + 1):x2k + 2 - y2k + 2


⇒ x2k.x2 - y2k + 2


⇒ [y2k + m(x + y)]x2 - y2k + 2 From equation(1)


⇒ m(x + y)x2 + y2k(x2 - y2)


⇒ m(x + y)x2 + y2k(x - y)(x + y)


⇒ (x + y)[mx2 + y2k(x - y)]


We proved that P(k + 1) is true.


Hence by the principle of mathematical induction, it is true for all n ∈ N.


Question 22.

Prove the following using the principle of mathematical induction for all n ∈ N

32n + 2 – 8n – 9 is divisible by 8.


Answer:

Let the given statement be P(n), as


P(n):32n + 2 - 8n - 9 is divisible by 8.


First, we check if it is true for n = 1,


P(1):34 - 8 - 9 = 81 - 17 = 64 = 8(8);


∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


P(k):32k + 2 - 8k - 9 = 8m where m ∈ N.


32k + 2 = 8k + 9 + 8m ………….(1)


We shall prove that P(k + 1)is true,


P(k + 1):32k + 4 - 8(k + 1) - 9


⇒ 32k + 2.32 - 8k - 8 - 9


⇒ (8k + 9 + 8m)9 - 8k - 17 From equation(1)


⇒ 64k + 72m + 81 - 17


⇒ 64k + 72m + 64


⇒ 8(8k + 9m + 8)


We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 23.

Prove the following using the principle of mathematical induction for all n ∈ N

41n – 14n is a multiple of 27.


Answer:

Let the given statement be P(n), as


P(n):41n - 14n is divisible by 27.


First, we check if it is true for n = 1,


P(1):411 - 141 = 27;


∴ It is true for n = 1.


Now we assume that it is true for some positive integer k, such that


P(k):41k - 14k = 27m where m ∈ N.


41k = 14k + 27m ………….(1)


We shall prove that P(k + 1)is true,


P(k + 1):41k + 1 - 14k + 1


⇒ 41k.41 - 14k + 1


⇒ (14k + 27m)41 - 14k + 1 From equation(1)


⇒ 27.41m + 14k(41 - 14)


⇒ 27.41m + 14k.27


⇒ 27(41m + 14k)


We proved that P(k + 1) is true.


Hence by principle of mathematical induction it is true for all n ∈ N.



Question 24.

Prove the following using the principle of mathematical induction for all n ∈ N

(2n + 7) < (n + 3)2.


Answer:

Let the given statement be P(n), as

P(n):(2n + 7) < (n + 3)2

Steps for Proving By Mathematical Induction:

Step 1: Verify that P(1) is true.


Step 2: If P(k) is true then P(k + 1) is also true.


Step 1:

First, we check if it is true for n = 1,

P(1): (2 + 7) < (4)2;

∴ It is true for n = 1.

Step 2:

Now we assume that it is true for some positive integer k, such that

P(k):(2k + 7) < (k + 3)2 .......(1)

We shall prove that P(k + 1)is true,

⇒ P(k + 1) = (2 (k + 1) + 7) < ( (k + 1) + 3)2

P(k + 1): 2(k + 1) + 7 < (k + 4)2

Now From Equation (1) adding 2 on both the sides we get,

⇒ (2k + 7) + 2 < (k + 3)2 + 2


⇒ 2(k + 1) + 7 < k2 + 6k + 11


⇒ 2(k + 1) + 7 < k2 + 6k + 11 + (2k + 5)


⇒ 2(k + 1) + 7 < k2 + 8k + 16


⇒ 2(k + 1) + 7 < (k + 4)2


We proved that P(k + 1) is true.


Hence by the principle of mathematical induction, it is true for all n ∈ N.