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