Let p = ln(x), q = ln(x3) and r = ln(x5), where x > 1. Which of the following statements is/are correct? 

I. p, q and r are in AP.

Il. p, q and r can never be in GP.

Select the answer using the code given below.  

This question was previously asked in
NDA-II 2024 (Maths) Official Paper (Held On: 01 Sept, 2024)
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  1. I only 
  2. II only 
  3. Both I and II
  4. Neither I nor II 

Answer (Detailed Solution Below)

Option 3 : Both I and II
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Detailed Solution

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Concept:

Arithmetic Progression (AP):

  • The terms are in AP if the difference between consecutive terms is constant.
  • The common difference is given by: \(d = q - p = r - q\)

Geometric Progression (GP):

  • The terms are in GP if the ratio between consecutive terms is constant.
  • The common ratio is given by: \(r = q \times p\)

Calculation:

Given

p = ln(x),

q = ln(x3)  = 3 lnx

and r = ln(x5) = 5 lnx

Clearly, p - q  = r - q = \(2lnx\)

⇒ p, q, r are in AP

Also \(\frac{q}{p} ≠ \frac{r}{p} \because \frac{q}{p} = 3 , \frac{r}{p} = \frac{5}{3}\)

∴ p, q, r can never be in GP

∴ Option (c) is correct.

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