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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 when only the first term
a
a
a
and the last term
l
l
l
are known? a)
n
2
(
2
a
+
l
)
\dfrac{n}{2}\,(2a + l)
2
n
(
2
a
+
l
)
b)
n
2
(
a
+
l
)
\dfrac{n}{2}(a + l)
2
n
(
a
+
l
)
c)
n
(
a
+
l
)
n(a + l)
n
(
a
+
l
)
d)
n
2
(
a
−
l
)
\dfrac{n}{2}(a - l)
2
n
(
a
−
l
)
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