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Mathematics
Mathematics
Problem
Simplify
∑
k
=
1
n
(
5
k
+
7
)
−
5
∑
k
=
1
n
k
\displaystyle \sum_{k=1}^{n} (5k + 7)\; - \; 5\sum_{k=1}^{n} k
k
=
1
∑
n
(
5
k
+
7
)
−
5
k
=
1
∑
n
k
for a positive integer
n
n
n
. a)
12
n
12n
12
n
b)
7
n
7n
7
n
c)
7
(
n
+
1
)
7(n+1)
7
(
n
+
1
)
d)
7
n
2
\dfrac{7n}{2}
2
7
n
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