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If the nth term of GP 5,52,54,58,... is 51024 then the value of n is
a) 11
b) 10
c) 9
d) 4

Answer
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Hint: Here we have to the nth term of the sequence. The sequence is an infinite sequence. First we have to determine the kind of a sequence and then we have a formula for the nth term and then by substituting the values we determine the solution for the question.

Complete step by step answer:
In mathematics we have three types of series namely, arithmetic series, geometric series and harmonic series.
First we have to determine the kind of the sequence.
Suppose if the sequence is an arithmetic sequence, then we have to check the common difference. The a1=5,a2=52,a3=54,a4=58.Let we determine the difference between first two terms d1=a2a1=525=152and we determine the difference between the next two terms d2=a3a2=54+52=308. Hence d1d2. Therefore the given sequence is not an arithmetic sequence.
Suppose if the sequence is a geometric sequence, then we have to check the common ratio. The a1=5,a2=52,a3=54,a4=58.Let we determine the ratio between first two terms r1=a2a1=525=52×15=12and we determine the difference between the next two terms r2=a3a2=5452=54×25=12. Hence r1=r2. Therefore the given sequence is a geometric sequence.

The geometric series is defined as the series with a constant ratio between the two successive terms. The finite geometric series is generally represented as a,ar,ar2,...,arn, where a is first term and r is a common ratio.
The nth term of the given sequence is given by Tn=arn1, where Tnrepresents the nth term. The a is the first term and it is 5. The r is the common ratio and it is r=12.
Therefore the nth term is given by Tn=5.(12)n1. We have the term 51024
So we have
51024=5(12)n1
On cancelling the number 5 we have
11024=1(12)n1
(12)10=(12)n1
(12)10=(12)n1
On equating the powers we have
n1=10
n=11
Therefore, n=11. Hence, option (a) is the correct option.

Note:
We must know about the geometric progression arrangement and it is based on the first term and common ratio. The common ratio of the geometric progression is defined as a2a1 where a2 represents the second term and a1 represents the first term. The sum of n terms is defined on the basis of common ratio.