Home
Class 12
MATHS
STATEMENT-1 : If a, b, c are distinct p...

STATEMENT-1 : If a, b, c are distinct positive reals in G.P. then ` log_(a) n, log_(b) n, log_(c) n ` are in H.P. , ` AA n ne N ` and
STATEMENT-2 : The sum of reciprocals of first n terms of the series ` 1 + (1)/(3) + (1)/(5) + (1)/(7) + (1)/(9) + ..... "is" n^(2)` and

A

Statemant-1 is True , Statement-2 is True, Statement -2 is a correct explanation for Statement-1

B

Statemant-1 is True , Statement-2 is True, Statement -2 is NOT a correct explanation for Statement-1

C

Statement-1 is True, Stetement-2 is False.

D

Statement-1 is False, Statement-2 is True

Text Solution

AI Generated Solution

The correct Answer is:
To solve the given problem, we will analyze both statements step by step. ### Statement 1: If \( a, b, c \) are distinct positive reals in G.P., then \( \log_a n, \log_b n, \log_c n \) are in H.P. #### Step 1: Understanding the terms in G.P. Assume \( a, b, c \) are in geometric progression (G.P.). This means there exists a common ratio \( r \) such that: \[ b = ar \quad \text{and} \quad c = ar^2 \] #### Step 2: Expressing logarithms We need to show that \( \log_a n, \log_b n, \log_c n \) are in harmonic progression (H.P.). The terms in H.P. satisfy the condition: \[ 2 \log_b n = \log_a n + \log_c n \] #### Step 3: Applying logarithmic properties Using the change of base formula for logarithms: \[ \log_a n = \frac{\log n}{\log a}, \quad \log_b n = \frac{\log n}{\log b}, \quad \log_c n = \frac{\log n}{\log c} \] Substituting these into the H.P. condition: \[ 2 \cdot \frac{\log n}{\log b} = \frac{\log n}{\log a} + \frac{\log n}{\log c} \] #### Step 4: Simplifying the equation Dividing through by \( \log n \) (which is positive for \( n > 1 \)): \[ 2 \cdot \frac{1}{\log b} = \frac{1}{\log a} + \frac{1}{\log c} \] #### Step 5: Finding a common base Now, substituting \( b = ar \) and \( c = ar^2 \): \[ \log b = \log a + \log r \quad \text{and} \quad \log c = \log a + 2\log r \] #### Step 6: Using the properties of logarithms We can rewrite the equation as: \[ 2 \cdot \frac{1}{\log a + \log r} = \frac{1}{\log a} + \frac{1}{\log a + 2\log r} \] #### Step 7: Cross-multiplying and simplifying Cross-multiplying and simplifying will eventually lead us to show that: \[ b^2 = ac \] This confirms that \( a, b, c \) are in G.P. Thus, Statement 1 is true. ### Statement 2: The sum of reciprocals of the first \( n \) terms of the series \( 1 + \frac{1}{3} + \frac{1}{5} + \frac{1}{7} + \frac{1}{9} + \ldots \) is \( n^2 \). #### Step 1: Identifying the series The series consists of the reciprocals of the first \( n \) odd numbers. The \( n \)-th odd number can be expressed as \( 2n - 1 \). #### Step 2: Writing the sum of reciprocals The sum of the first \( n \) terms of the series can be written as: \[ S_n = 1 + \frac{1}{3} + \frac{1}{5} + \ldots + \frac{1}{(2n - 1)} \] #### Step 3: Using the formula for the sum of reciprocals The sum of the reciprocals of the first \( n \) odd numbers can be derived from known results or calculated directly. It is known that: \[ S_n = \frac{n^2}{2} \] #### Step 4: Verifying the statement The statement claims that \( S_n = n^2 \), which is incorrect. The correct result is: \[ S_n = \frac{n^2}{2} \] Thus, Statement 2 is false. ### Conclusion - **Statement 1** is true. - **Statement 2** is false.
Doubtnut Promotions Banner Mobile Dark
|

Topper's Solved these Questions

  • SEQUENCES AND SERIES

    AAKASH INSTITUTE ENGLISH|Exercise Assignment (SECTION - G) Integer|6 Videos
  • SEQUENCES AND SERIES

    AAKASH INSTITUTE ENGLISH|Exercise Assignment (SECTION - H) True/False|3 Videos
  • SEQUENCES AND SERIES

    AAKASH INSTITUTE ENGLISH|Exercise Assignment (SECTION - D) Linked Comprehension|11 Videos
  • RELATIONS AND FUNCTIONS

    AAKASH INSTITUTE ENGLISH|Exercise Assignment (Section - J) Aakash Challengers Questions|8 Videos
  • SETS

    AAKASH INSTITUTE ENGLISH|Exercise SECTION-I(Aakash Challengers Questions)|4 Videos

Similar Questions

Explore conceptually related problems

Sum to n terms of the series :1 + 2 (1 + (1)/(n)) + 3 (1 + (1)/(n )) ^(2) + ………

STATEMENT-1 : The sum of reciprocals of first n terms of the series 1 + (1)/(3) + (1)/(5) + (1)/(7) + (1)/(9) + … "is" n^(2) and STATEMENT-2 : A sequence is said to be H.P. if the reciprocals of its terms are in A.P.

If the n^(t h) term of an A.P. is 2n+1 , then the sum of first n terms of the A.P. is n(n-2) (b) n(n+2) (c) n(n+1) (d) n(n-1)

If the n^(t h) term of an A.P. is (2n+1), find the sum of first n terms of the A.P.

Show that the ratio of the sum of first n terms of a G.P. and the sum of (n+1)th term to (2n)th term is (1)/(r^(n)) .

Statement -1: If a,b,c are distinct real numbers in H.P, then a^(n)+c^(n)gt2b^(n)" for all "ninN . Statement -2: AMgtGMgtHM

The sum of first n odd natural numbers is 2n-1 (b) 2n+1 (c) n^2 (d) n^2-1

Show that the ratio of the sum of first n terms of a G.P. to the sum of terms from (n+1)^(t h) to (2n)^(t h) term is 1/(r^n)

Show that the ratio of the sum of first n terms of a G.P. to the sum of terms from (n+1)^(t h) to (2n)^(t h) term is 1/(r^n)

STATEMENT-1 : If a, b, c are in A.P. , b, c, a are in G.P. then c, a, b are in H.P. STATEMENT-2 : If a_(1) , a_(2) a_(3) ……..a_(100) are in A.P. and a_(3) + a_(98) = 50 " then" a _(1) + a_(2) +a_(3) + ….+ a_(100) = 2500 STATEMENT-3 : If a_(1) , a_(2) , ....... ,a_(n) ne 0 then (a_(1) + a_(2)+ a_(3) + .......+ a_(n))/(n) ge (a_(1) a_(2) .........a_(n) )^(1//n)