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Byju's Answer
Standard XII
Mathematics
Summation by Sigma Method
13+12+1+23+22...
Question
1
3
+
1
2
+
1
+
2
3
+
2
2
+
2
+
3
3
+
3
2
+
3
+
.
.
.
3
n
terms
=
A
n
(
n
+
1
)
(
n
2
+
12
n
+
5
)
12
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B
n
(
n
+
1
)
(
3
n
2
+
7
n
+
8
)
12
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C
n
(
n
+
1
)
(
n
+
2
)
(
n
2
+
5
n
+
6
)
12
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D
(
n
+
1
)
(
n
+
2
)
(
n
+
3
)
4
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Solution
The correct option is
B
n
(
n
+
1
)
(
3
n
2
+
7
n
+
8
)
12
S
=
Σ
r
3
+
Σ
r
2
+
Σ
r
S
=
n
2
(
n
+
1
)
2
4
+
n
(
n
+
1
)
(
2
n
+
1
)
6
+
n
(
n
+
1
)
2
S
=
n
(
n
+
1
)
(
3
n
2
+
7
n
+
8
)
12
Hence Option B
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Q.
The sum of the series
1
2
.2 +
2
2
.3 +
3
2
.4 + ........ to n terms is