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Question

Question: If log 2, \(\log(2^{n} - 1)\) and \(\log(2^{n} + 3)\) are in A.P., then *n* =...

If log 2, log(2n1)\log(2^{n} - 1) and log(2n+3)\log(2^{n} + 3) are in A.P., then n =

A

5/2

B

log25\log_{2}5

C

log35\log_{3}5

D

32\frac{3}{2}

Answer

log25\log_{2}5

Explanation

Solution

As, log 2, log(2n1)\log(2^{n} - 1) and log(2n+3)\log(2^{n} + 3) are in A.P. Therefore

2log(2n1)=log2+log(2n+3)2\log(2^{n} - 1) = \log 2 + \log(2^{n} + 3)(2n5)(2n+1)=0(2^{n} - 5)(2^{n} + 1) = 0

As 2n2^{n} cannot be negative, hence 2n5=02^{n} - 5 = 02n=52^{n} = 5 or

n=log25n = \log_{2}5