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Byju's Answer
Standard XII
Mathematics
AM,GM,HM Inequality
Given that ...
Question
Given that
1
+
x
+
x
2
+
⋯
x
n
−
1
=
1
−
x
n
1
−
x
,
x
≠
1
, Using this, find the sum of the series
1
+
2
x
+
3
x
2
+
⋯
(
n
−
1
)
x
n
−
2
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Solution
1
+
x
+
x
2
+
⋯
+
x
n
−
1
=
1
−
x
n
1
−
x
Differentiating on both sides with respect to
x
1
+
2
x
+
3
x
2
+
⋯
+
(
n
−
1
)
x
n
−
2
=
(
1
−
x
)
(
−
n
x
n
−
1
)
+
1
−
x
n
(
1
−
x
)
2
=
(
n
−
1
)
x
n
−
n
x
n
−
1
+
1
(
1
−
x
)
2
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