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© examsnet.com
Question : 36
Total: 79
What is the fourth term of an AP of n terms whose sum is n (n+1) ?
[NDA I 2019]
6
8
12
20
Validate
Solution:
(B)
Given
S
n
=
n
(
n
+
1
)
, we known
T
n
=
S
n
−
S
n
−
1
T
n
= n(n+1) − (n−1)n
⇒
T
n
= 2n
⇒
T
4
= 8
© examsnet.com
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