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Mathematics
Mathematics
Problem
The sum
∑
k
=
4
n
+
3
(
10
−
k
)
\displaystyle \sum_{k=4}^{n+3}(10 - k)
k
=
4
∑
n
+
3
(
10
−
k
)
can be rewritten in the standard form
∑
j
=
1
n
(
A
+
(
j
−
1
)
D
)
\displaystyle \sum_{j=1}^{n} \bigl(A + (j-1)D\bigr)
j
=
1
∑
n
(
A
+
(
j
−
1
)
D
)
. Which pair
(
A
,
D
)
(A,D)
(
A
,
D
)
is correct? a)
(
7
,
−
1
)
(7,\,-1)
(
7
,
−
1
)
b)
(
10
,
−
1
)
(10,\,-1)
(
10
,
−
1
)
c)
(
6
,
−
1
)
(6,\,-1)
(
6
,
−
1
)
d)
(
6
,
1
)
(6,\,1)
(
6
,
1
)
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