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UPSC NDA 2 2019 Mathematics Solved Paper
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© examsnet.com
Question : 4
Total: 120
If the sum of first n terms of a series is (n + 12), then what is its third term?
[NDA II 2019]
1
2
3
4
Validate
Solution:
👈: Video Solution
Given,
S
n
=
n
+
12
∵
T
n
=
S
n
−
S
n
−
1
∴
T
3
=
S
3
−
S
3
−
1
⇒
T
3
=
S
3
–
S
2
⇒
T
3
=
(
3
+
12
)
–
(
2
+
12
)
⇒
T
3
=
15
–
14
⇒
T
3
=
1
Hence, third term = 1
© examsnet.com
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