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If  then
a)| a | ≥ 1 
b)| a | ≤ 1
c)| a | > 1
d)| a | < 1
Correct answer is option 'D'. Can you explain this answer?

Chirag Verma answered
Correct Answer :- D
Explanation : For |a|<1 
b = 1/a, |b|>1 
lim (n→∞) an = lim (n→∞) (1/b)n
= lim(n→∞) 1/bn
= 1/(±∞)
= 0
 

A convergent sequence is a Cauchy sequence, if it is a
  • a)
    sequence of real numbers
  • b)
    sequence of rational numbers
  • c)
    sequence of irrational numbers
  • d)
    None of the above
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
ANSWER :- b
Solution :- If {an}∞n=1 is a cauchy sequence of real numbers and if there is a sub-sequence of this sequence, {anj}∞j=1 which converges to a real number L, then I need to show that the sequence {an}∞n=1 converges to the real number L.

The sequence {xn}, where xn = nl/n, converge to
  • a)
    1
  • b)
    0
  • c)
    1/2
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

One can view the sequence as a function and take log on both sides and evaluate using l'hospital rule.

The sequence <sn> =  is 
  • a)
    not monotonic but bounded
  • b)
    not monotonic and not bounded
  • c)
    monotonic but not bounded
  • d)
    monotonic and bounded
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered
Here lower bound = l = − 1/2 , & upper bounded u = 1. But the given sequence is neither increasing nor decreasing. Thus, <sn> is bounded but not monotonic.

If Sn denoted the sum of n term of the series 
  • a)
    Sn > n2
  • b)
    Sn > n
  • c)
  • d)
    Sn = ∞
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered
If Sn denote the sum of n terms of the series  then Sn will be > Explanation:

A: Sn > n^2
- The given comparison tells us that the sum of the first n terms of the series is greater than n^2.
- This could be true for certain series where the sum of terms grows faster than n^2, such as series with exponential growth.
- However, this comparison alone does not provide enough information to determine the behavior of the series for all values of n.

B: Sn > n
- This comparison indicates that the sum of the first n terms of the series is greater than n itself.
- Similar to the first comparison, this could be true for certain series with increasing terms.
- Again, this comparison alone does not give a definitive answer about the convergence or divergence of the series.

C: Sn = ∞
- This comparison suggests that the sum of the terms of the series diverges to infinity.
- If the sum of the series approaches infinity as n increases, it indicates that the series does not converge.
- This comparison implies that the series may be divergent and does not have a finite sum.

D: Sn = ∞
- This comparison reiterates the previous point that the sum of the series diverges to infinity.
- It reinforces the idea that the series does not have a finite sum and diverges as n increases.

Conclusion:
- Based on the comparisons provided, it is most likely that the series described does not converge and has an infinite sum. This is indicated by the comparisons stating that the sum of the terms exceeds n^2 and n, and ultimately diverges to infinity.

The series 2 + 4 + 6 + 8 + ...is
  • a)
    divergent
  • b)
    convergent
  • c)
    Both of these
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered

The sequence of n th partial sum of given series is unbounded and goes to infinity.
since sequence of n th partial sum is unbounded, it is not convergent therefore the given series
is not convergent i.e. divergent.

For the sequence 1, 7, 25, 79, 241, 727 … simple formula for {an} is ____________ 
  • a)
    3n+1 – 2 
  • b)
    (-3)n + 4
  • c)
    n2 – 2
  • d)
    3n – 2 
Correct answer is option 'D'. Can you explain this answer?

Chirag Verma answered
The ratio of consecutive numbers is close to 3. Comparing these terms with the sequence of {3n} which is 3, 9, 27 …. Comparing these terms with the corresponding terms of sequence {3n} and the nth term is 2 less than the corresponding power of 3.

Match list I with list II and select the correct answer

  • a)
    a
  • b)
    b
  • c)
    c
  • d)
    d
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered


is also convergent series.
∴ un is also convergent series.

Hence, by d’Alembert test 

implies un is divergent series.

By Cauchy condensation test, ∑μn is convergent series.
(D) 
By Leibnitz’s test, the series is convergent.
Also,  is divergent series. 
So, the given series is converges conditionally.

  • a)
    is not bounded
  • b)
    may or may not be bounded
  • c)
    convergent
  • d)
    may or may not be convergent
Correct answer is option 'A'. Can you explain this answer?

Simply by cauchy second theorem on limits if lim Sn = l, then lim Sn/n= l also.

Therefore here Sn= l and is convergent to L. option c is correct

The series 
  • a)
    conditional convergent
  • b)
    absolutely convergent
  • c)
    divergent
  • d)
    None of the above
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered
Let the given series be denoted by ∑μn, then
∑|μn|

Compare this series ∑vn with the auxiliary series,

Then,

which is finite quantity.
Hence, ∑un and ∑wn are either both convergent or both divergent. But ∑wn 

Hence, the series ∑vn is divergent.
Also, in the series ∑un, we find that its term are alternately positive and negative, its terms are continuously decreasing and

Thus, all condition of Leibnitz’s test are satisfied and as such ∑un is convergent. H ence, the given series ∑un is conditionally convergent.

The sequence 
  • a)
    divergent
  • b)
    convergent to 0
  • c)
    convergent to 1
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered
Correct Answer :- b
Explanation : Suppose otherwise, that there exists a number L implies R and a positive integer N such that
| f(n) - L | < e {for all } e > 0 {for all } n > N. 
Since N is a positive integer, we know 4N > N and 4N+2 > N. 
But,
f(4N) = cos (2N pi) = 1 and f(4N+2) = cos((2N+1)pi) = -1
Taking e = 1/2 
= |1 - L| < 1/2 and |-1-L| < 1/2 
=> |1+L| < 1/2
But, these imply
|1-L| + |1+L| < 1.
By the triangle inequality we then have
|1 - L + 1 + L | < 1
=> 2 < 1
a contradiction. Hence, there is no such limit L.
Therefore, the sequence converges to zero.

If {xn} and {yn} are two convergent sequence such that xn < yn,  n ∈ N, then
  • a)
  • b)
  • c)
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered
The correct option is Option A.
Let lim xn = x and lim yn = y and zn = yn - xn
      n->∞                n->∞
Then (zn) is a convergent sequence such that zn > 0 ∇ n ∊N
and lim zn = y - x. 
       n->∞
Now (zn) is a convergent sequence of real numbers and zn > 0 ∇ n ∊N
So, lim zn ≥ 0
      n->∞
So, y - x ≥ 0
     => y ≥ x
     => lim yn ≥ lim xn
          n->∞      n->∞
 
Hence, proved.

If a sequence is not a Cauchy sequence, then it is a  
  • a)
    divergent sequence
  • b)
    convergent sequence
  • c)
    bounded sequence
  • d)
    None of the above
Correct answer is option 'A'. Can you explain this answer?

A sequence that is not a Cauchy sequence is called a divergent sequence. A Cauchy sequence is a sequence whose elements get closer and closer together as the sequence progresses. 

The series
  • a)
    convergent
  • b)
    divergent
  • c)
    oscillatory
  • d)
    None of these
Correct answer is option 'B'. Can you explain this answer?

Chirag Verma answered



which is finite and non-zero.
Since, ∑vn is divergent, therefore, ∑un is also divergent.

  • a)
  • b)
  • c)
     
  • d)
Correct answer is option 'C'. Can you explain this answer?

Veda Institute answered
Here, it is given that 


Hence, ∑vn is divergent and ∑un is also divergent and 


Find the sum of the series. 
  • a)

    (1/3)ln2−5/18
  • b)
     
    (1/3)ln2−5/6
  • c)
     
    (2/3)ln2−5/18
  • d)
     
    (2/3)ln2−5/6
Correct answer is option 'C'. Can you explain this answer?

Pie Academy answered
This problem is a very basic one, this problem can easily be solved by step by step solution. The steps are:
Step 1 : First we will ignore the summation part. We will factorize the denominator, because we are going step by step so our aim is to simplify the given problem first.
Step 2: After factorizing the the denominator we will reach to a position where we have to use partial fraction to go forward.
Step 3: In this step we will take care of the (−1)�� part, like how it will affect the series.
Step 4: After taking care of the (−1)�� we will now expand the summation (breaking it into infinite sum).
Step 5 : So after 4 steps we are halfway done now just the last simplification is left we will use the value
ln2=1−1/2+1/3−1/4+…

The series 
  • a)
    oscillating
  • b)
    convergent
  • c)
    unbounded
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered
or 0 as n is odd or even implies {Sn} - { 1 , 0 , 1 , 0 , . . . }
It is an oscillating sequence

The sequence {Sn} of real numbers given by Sn = is
  • a)
    a divergent sequence
  • b)
    a Cauchy sequence
  • c)
    an oscillatory sequence
  • d)
    not a Cauchy sequence
Correct answer is option 'B'. Can you explain this answer?

Veda Institute answered

So <Sn> is monotonically increasing Next, we will show that it is bounded.

⇒ <Sn> is bounded. By the theorem's Every monotonic bounded sequence is convergent, Then <Sn> is convergent.
By the Lemma, if <Sn> is a convergent sequence of real numbers, Then <Sn> is a Cauchy-sequence.
 

The series  convergent, if
  • a)
    |x |≤ 1
  • b)
    |x|≤2
  • c)
    |x| > 2
  • d)
    | x | ≥ 4
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered
Here given series is  is convergent

∴ The given series will be convergent, if



Hence, vn is convergent series, so un is also convergent.
∴ The given series is convergent, if | x | ≤ 1.

The interval of convergence of is
  • a)
    (–1, 1)
  • b)
    [–1, 1) 
  • c)
    [-1, -1]
  • d)
    [–1, 1] 
Correct answer is option 'D'. Can you explain this answer?

Chirag Verma answered

R = 1 / P = 1 = radius of convergence
When x = 1 & x = –1, Then is converges at both 
x = 1 & x = – 1.
so, its interval of convergence is exactly [–1, 1].

The series whose nth term is 
  • a)
    converges to the sum 0
  • b)
    converges to the sum 1/2
  • c)
    converges to the sum 1
  • d)
    diverges
Correct answer is option 'D'. Can you explain this answer?

Chirag Verma answered
Here it is given that

Now, taking auxiliary series 

Which is finite and non-zero. Since, vn is divergent.
Hence, tn is also divergent.

Which one of the following is incorrect?
  • a)
    every bounded sequence has a convergent subsequence
  • b)
    every sequence has a monotonic subsequence
  • c)
    every sequence has a limit point
  • d)
    every sequence has a countable number of terms
Correct answer is option 'C'. Can you explain this answer?

Chirag Verma answered
Solution :

The 
set of all cluster points
 of a sequence is sometimes called the limit set. contains all but finitely many elements of the sequence). That is why we do not use the term limit point of a sequence as a synonym for accumulation point of the sequence.

In the given AP series the term at position 11 would be? 5, 8, 11, 14, 17, 20.........50. 
  • a)
    45 
  • b)
    25 
  • c)
    15
  • d)
    35 
Correct answer is option 'D'. Can you explain this answer?

Ayush Gupta answered
Explanation:

An arithmetic progression (AP) is a sequence of numbers in which the difference between any two consecutive terms is constant. In this case, the common difference is 3, as each term is obtained by adding 3 to the previous term.

Finding the 11th term:
To find the 11th term in the given AP series, we can use the formula for the nth term of an AP:

a_n = a + (n - 1)d

Where:
a_n is the nth term,
a is the first term,
n is the position of the term,
d is the common difference.

In this case:
a = 5 (the first term),
n = 11 (the position of the term),
d = 3 (the common difference).

Substituting the values into the formula:
a_n = 5 + (11 - 1) * 3
= 5 + (10) * 3
= 5 + 30
= 35

Therefore, the 11th term in the given AP series is 35.

Conclusion:
The 11th term in the given AP series is 35, so the correct answer is option D.

The series 13 + 23 + 33 + .... is 
  • a)
    divergent
  • b)
    convergent
  • c)
    bounded
  • d)
    None of these
Correct answer is option 'A'. Can you explain this answer?

Chirag Verma answered

{Sn} is increasing sequence and unbounded from above.
∴ It is divergent sequence.
Hence, the series is divergent series.

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