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Mathematics
Problem
Let
a
1
,
a
2
,
a
3
…
a_1, a_2, a_3 \dots
a
1
,
a
2
,
a
3
…
be in an A.P. such that
∑
k
=
1
12
a
2
k
−
1
=
−
72
5
a
1
\sum_{k=1}^{12} a_{2k-1} = -\frac{72}{5}a_1
∑
k
=
1
12
a
2
k
−
1
=
−
5
72
a
1
,
a
1
≠
0
a_1 \neq 0
a
1
=
0
. If
∑
k
=
1
n
a
k
=
0
\sum_{k=1}^{n} a_k = 0
∑
k
=
1
n
a
k
=
0
, then
n
n
n
is: (1) 11 (2) 10 (3) 18 (4) 17
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