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2023 ISL
A7
The Return of Triangle Geometry
The Return of Triangle Geometry
Source: 2023 ISL A7
July 17, 2024
Problem Statement
Let
N
N
N
be a positive integer. Prove that there exist three permutations
a
1
,
…
,
a
N
a_1,\dots,a_N
a
1
,
…
,
a
N
,
b
1
,
…
,
b
N
b_1,\dots,b_N
b
1
,
…
,
b
N
, and
c
1
,
…
,
c
N
c_1,\dots,c_N
c
1
,
…
,
c
N
of
1
,
…
,
N
1,\dots,N
1
,
…
,
N
such that
∣
a
k
+
b
k
+
c
k
−
2
N
∣
<
2023
\left|\sqrt{a_k}+\sqrt{b_k}+\sqrt{c_k}-2\sqrt{N}\right|<2023
a
k
+
b
k
+
c
k
−
2
N
<
2023
for every
k
=
1
,
2
,
…
,
N
k=1,2,\dots,N
k
=
1
,
2
,
…
,
N
.
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