find the sum of the 9 terms of the series 7,14,21,..
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Answer:
We need to start by finding the number of terms,
n
.
The formula
t
n
=
a
+
(
n
−
1
)
d
gives the nth term of an arithmetic series.
98
=
7
+
(
n
−
1
)
7
98
=
7
+
7
n
−
7
7
n
=
98
n
=
14
We can now apply the formula
s
n
=
n
2
(
t
1
+
t
n
)
to determine the sum of the series.
s
14
=
14
2
(
7
+
98
)
s
14
=
7
(
105
)
s
14
=
735
Step-by-step explanation:
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