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Polish MO Finals
1974 Polish MO Finals
1
1
Part of
1974 Polish MO Finals
Problems
(1)
plane _|_ CD , in tetrahedron ABCD
Source: Polish MO Finals 1974 p1
8/23/2024
In a tetrahedron
A
B
C
D
ABCD
A
BC
D
the edges
A
B
AB
A
B
and
C
D
CD
C
D
are perpendicular and
∠
A
C
B
=
∠
A
D
B
\angle ACB =\angle ADB
∠
A
CB
=
∠
A
D
B
. Prove that the plane through
A
B
AB
A
B
and the midpoint of the edge
C
D
CD
C
D
, is perpendicular to
C
D
CD
C
D
.
geometry
3D geometry
tetrahedron