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Byju's Answer
Standard XII
Mathematics
Sigma n2
Let Sk=1+2+3+...
Question
Let
S
k
=
1
+
2
+
3
+
⋯
+
k
k
.
If
S
2
1
+
S
2
2
+
⋯
+
S
2
19
=
A
4
,
then the value of
A
is
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Solution
S
k
=
k
(
k
+
1
)
2
k
=
k
+
1
2
S
2
1
+
S
2
2
+
⋯
+
S
2
19
=
1
4
(
2
2
+
3
2
+
4
2
+
⋯
+
20
2
)
=
1
4
(
1
2
+
2
2
+
3
2
+
4
2
+
⋯
+
20
2
−
1
)
=
1
4
[
20
(
21
)
(
41
)
6
−
1
]
=
2869
4
∴
A
=
2869
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0
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Q.
Let
S
k
=
1
+
2
+
3
+
⋯
+
k
k
.
If
S
2
1
+
S
2
2
+
⋯
+
S
2
19
=
A
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,
then the value of
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is
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