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Putnam
1968 Putnam
A4
Putnam 1968 A4
Putnam 1968 A4
Source: Putnam 1968
February 19, 2022
Putnam
geometry
3D geometry
sphere
Problem Statement
Let
S
2
⊂
R
3
S^{2}\subset \mathbb{R}^{3}
S
2
⊂
R
3
be the unit sphere. Show that for any
n
n
n
points on
S
2
S^{2}
S
2
, the sum of the squares of the
n
(
n
−
1
)
2
\frac{n(n-1)}{2}
2
n
(
n
−
1
)
distances between them is at most
n
2
n^{2}
n
2
.
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