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Byju's Answer
Standard XII
Mathematics
Sum of n Terms
If a1,a2,a3...
Question
If
a
1
,
a
2
,
a
3
,
.
.
.
,
a
n
are in A.P of non-zero terms, Prove that
1
a
1
a
2
+
1
a
2
a
3
+
1
a
3
a
4
+
.
.
.
1
a
n
−
1
a
n
=
n
−
1
a
1
a
n
Open in App
Solution
Let
d
be the common difference of the A.P
∴
d
=
a
2
−
a
1
=
a
3
−
a
2
=
a
4
−
a
3
=
.
.
.
=
a
n
−
a
n
−
1
Given
1
a
1
a
2
+
1
a
2
a
3
+
1
a
3
a
4
+
.
.
.
1
a
n
−
1
a
n
n
−
1
a
1
a
n
=
1
d
(
d
a
1
a
2
+
d
a
2
a
3
+
d
a
3
a
4
+
.
.
.
d
a
n
−
1
a
n
n
−
1
a
1
a
n
)
=
1
d
(
a
2
−
a
1
a
1
a
2
+
a
3
−
a
2
a
2
a
3
+
a
4
−
a
3
a
3
a
4
+
.
.
.
a
n
−
a
n
−
1
a
n
−
1
a
n
n
−
1
a
1
a
n
)
=
1
d
(
a
2
a
1
a
2
−
a
1
a
1
a
2
+
a
3
a
2
a
3
−
a
2
a
2
a
3
+
.
.
.
+
a
n
a
n
−
1
a
n
−
a
n
−
1
a
n
−
1
a
n
)
=
1
d
[
1
a
1
−
1
a
2
+
1
a
2
−
1
a
3
+
.
.
.
+
1
a
n
−
1
−
1
a
n
]
=
1
d
[
1
a
1
−
1
a
n
]
=
1
d
[
a
n
−
a
1
a
1
a
n
]
=
1
d
[
a
1
+
(
n
−
1
)
d
−
a
1
a
1
a
n
]
=
n
−
1
a
1
a
n
Hence proved.
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0
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.
.
.
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3
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3
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√
a
4
+
.
.
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+
a
n
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1
√
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n
+
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If the set of non zero numbers
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a
1
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a
2
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1
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