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International Zhautykov Olympiad
2017 International Zhautykov Olympiad
3
Tetrahedron inequality
Tetrahedron inequality
Source: Izho 2017 P6
January 15, 2017
geometry
3D geometry
tetrahedron
inequalities
Problem Statement
Let
A
B
C
D
ABCD
A
BC
D
be the regular tetrahedron, and
M
,
N
M, N
M
,
N
points in space. Prove that:
A
M
⋅
A
N
+
B
M
⋅
B
N
+
C
M
⋅
C
N
≥
D
M
⋅
D
N
AM \cdot AN + BM \cdot BN + CM \cdot CN \geq DM \cdot DN
A
M
⋅
A
N
+
BM
⋅
BN
+
CM
⋅
CN
≥
D
M
⋅
D
N
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