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Mathematics
Problem
Prove that the sum
S
n
S_n
S
n
of the first
n
n
n
terms of a geometric progression with first term
a
a
a
and common ratio
r
≠
1
r\neq1
r
=
1
is
S
n
=
a
(
1
−
r
n
)
1
−
r
.
S_n=\dfrac{a(1-r^{n})}{1-r}.
S
n
=
1
−
r
a
(
1
−
r
n
)
.
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