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12th Grade > Mathematics

PRINCIPLE OF MATHEMATICAL INDUCTION MCQs

Total Questions : 15 | Page 2 of 2 pages
Question 11. If n ∈ N, then 72n + 23n3.3n1 is always divisible by
 
  1.    25
  2.    35
  3.    45
  4.    None of these
 Discuss Question
Answer: Option A. -> 25
:
A
Putting n = 1 in 72n+23n3.3n1
=50, divisible by 25
Question 12. If n ∈ N, then x2n1+y2n1 is divisible by 
  1.    x + y
  2.    x - y
  3.    x2 + y2
  4.    x2+xy
 Discuss Question
Answer: Option A. -> x + y
:
A
x2n1+y2n1 is always contain equal odd power.
So it is always divisible by x + y.
Question 13. To find:
12+22+32...................+n2
  1.    =n32
  2.    >n32
  3.    >n33
  4.    =n33
 Discuss Question
Answer: Option C. -> >n33
:
C
Let n=1
n32=12;n33=13
Let n=2,12+22=5
n32=4;n33=83
Letn=3,12+22+32=14
n32=272;n33=9
Letn=4,12+22+32+42=30
n32=32;n33=643
12+22+32++n2>n33
P(n):12+22+32++n2>n33
P(1) is true
Let P(k) be true.
12+22+32++k2>k33
12+22+32++k2+(k+1)2>k33+k2+2k+1
=k3+3k2+6k+33
=k3+3k2+3k+1+3k+23
=(k+1)33+k+23
12+22+32++k2+(k+1)2>(k+1)33
P(k+1) is true.
P(n) is true nN
Question 14. For all positive integral values of n, 32n - 2n + 1 is 
divisible by
  1.    2
  2.    4
  3.    8
  4.    12
 Discuss Question
Answer: Option A. -> 2
:
A
Putting n = 2 in 32n - 2n + 1 then,
32×2 - 2×2+1 = 81 - 4 + 1 = 78, which is divisible
by 2.
Question 15. For every positive integer n, 2n < n! when
  1.    n < 4
  2.    n≥ 4
  3.    n < 3
  4.    None of these
 Discuss Question
Answer: Option B. -> n≥ 4
:
B
Check through option, the condition 2n < n! is
true when n≥ 4.

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