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Power Series
hard
0:00.0
Determine the sum
∑
n
=
1
∞
n
(
n
−
1
)
2
n
\sum_{n=1}^{\infty} \frac{n(n-1)}{2^n}
∑
n
=
1
∞
2
n
n
(
n
−
1
)
.
A
1
B
2
C
4
D
8
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