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2023 China National Olympiad
2
Orz Orz Orz Orz Orz geometry
Orz Orz Orz Orz Orz geometry
Source: China MO 2023 P2
December 29, 2022
geometry
Problem Statement
Let
△
A
B
C
\triangle ABC
△
A
BC
be an equilateral triangle of side length 1. Let
D
,
E
,
F
D,E,F
D
,
E
,
F
be points on
B
C
,
A
C
,
A
B
BC,AC,AB
BC
,
A
C
,
A
B
respectively, such that
D
E
20
=
E
F
22
=
F
D
38
\frac{DE}{20} = \frac{EF}{22} = \frac{FD}{38}
20
D
E
=
22
EF
=
38
F
D
. Let
X
,
Y
,
Z
X,Y,Z
X
,
Y
,
Z
be on lines
B
C
,
C
A
,
A
B
BC,CA,AB
BC
,
C
A
,
A
B
respectively, such that
X
Y
⊥
D
E
,
Y
Z
⊥
E
F
,
Z
X
⊥
F
D
XY\perp DE, YZ\perp EF, ZX\perp FD
X
Y
⊥
D
E
,
Y
Z
⊥
EF
,
ZX
⊥
F
D
. Find all possible values of
1
[
D
E
F
]
+
1
[
X
Y
Z
]
\frac{1}{[DEF]} + \frac{1}{[XYZ]}
[
D
EF
]
1
+
[
X
Y
Z
]
1
.
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