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Mathematics
Problem
Which of the following expressions correctly gives the sum
S
n
S_n
S
n
of the first
n
n
n
terms of an arithmetic progression with first term
a
a
a
and common difference
d
d
d
? a)
S
n
=
n
2
[
a
+
(
n
−
1
)
d
]
S_n=\dfrac{n}{2}[a+(n-1)d]
S
n
=
2
n
[
a
+
(
n
−
1
)
d
]
b)
S
n
=
n
2
[
2
a
+
(
n
−
1
)
d
]
S_n=\dfrac{n}{2}[2a+(n-1)d]
S
n
=
2
n
[
2
a
+
(
n
−
1
)
d
]
c)
S
n
=
n
2
[
2
a
+
(
n
+
1
)
d
]
S_n=\dfrac{n}{2}[2a+(n+1)d]
S
n
=
2
n
[
2
a
+
(
n
+
1
)
d
]
d)
S
n
=
a
+
(
n
−
1
)
d
S_n=a+(n-1)d
S
n
=
a
+
(
n
−
1
)
d
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