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UPSC NDA I 2021 Mathematics Solved Paper
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© examsnet.com
Question : 8
Total: 120
The third term of a GP is 3 . What is the product of its first five terms?
[NDA-I 2021]
81
243
729
Cannot be determined due to insufficient data
Validate
Solution:
👈: Video Solution
Concept
Let us consider sequence
a
1
,
a
2
,
a
3
.
.
.
a
n
is an G.P.
Common ratio
=
r
=
a
2
a
1
=
a
3
a
2
=
a
n
a
n
−
1
Calculation:
Let a be the 3rd term of the G.P series,
So, we can write the five terms as,
a
r
2
,
a
r
,
a
,
a
r
,
a
r
2
So, the product of the five terms
=
a
5
Since
a
=
3
, the product of the first five terms
=
3
5
=
243
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