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Mathematics
Mathematics
Problem
Which of the following gives the sum of the first
n
n
n
terms of a geometric progression with first term
a
a
a
and common ratio
r
(
r
≠
1
)
r\,(r\neq1)
r
(
r
=
1
)
? a)
a
(
r
n
−
1
)
1
−
r
\dfrac{a(r^{n}-1)}{1-r}
1
−
r
a
(
r
n
−
1
)
b)
a
(
1
−
r
n
)
1
−
r
\dfrac{a(1-r^{n})}{1-r}
1
−
r
a
(
1
−
r
n
)
c)
a
(
1
−
r
n
−
1
)
1
−
r
\dfrac{a(1-r^{n-1})}{1-r}
1
−
r
a
(
1
−
r
n
−
1
)
d)
n
2
[
2
a
+
(
n
−
1
)
r
]
\dfrac{n}{2}\bigl[2a+(n-1)r\bigr]
2
n
[
2
a
+
(
n
−
1
)
r
]
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