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Mathematics
Problem
Which of the following expressions 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)
n
2
[
2
a
+
n
d
]
\dfrac{n}{2}\,[2a + nd]
2
n
[
2
a
+
n
d
]
b)
n
[
2
a
+
(
n
−
1
)
d
]
n\,[2a + (n-1)d]
n
[
2
a
+
(
n
−
1
)
d
]
c)
n
2
[
2
a
+
(
n
−
1
)
d
]
\dfrac{n}{2}\,[2a + (n-1)d]
2
n
[
2
a
+
(
n
−
1
)
d
]
d)
n
2
[
a
+
(
n
−
1
)
d
]
\dfrac{n}{2}\,[a + (n-1)d]
2
n
[
a
+
(
n
−
1
)
d
]
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