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NDA Math Sequences and Series
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© examsnet.com
Question : 71
Total: 79
The nth term of an A.P is
3
+
n
4
,then the sum of first 105 terms is
[NDA II 2015]
270
735
1409
1470
Validate
Solution:
T
n
=
3
+
n
4
S
n
=
∞
∑
n
=
0
T
n
=
∑
(
3
4
+
n
4
)
=
3
4
n
+
1
4
×
n
(
n
+
1
)
2
=
7
8
n
+
n
2
8
S
105
=
7
8
×
105
+
(
105
)
2
8
=
1470
© examsnet.com
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