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Polish Junior Math Olympiad
2021 Polish Junior Math Olympiad
2021 Polish Junior MO Second Round
2
2
Part of
2021 Polish Junior MO Second Round
Problems
(1)
<DEF = 90^o wanted, EF = DE in square ABCE (2021 Polish JMO R2 p2)
Source:
4/8/2021
Given is the square
A
B
C
D
ABCD
A
BC
D
. Point
E
E
E
lies on the diagonal
A
C
AC
A
C
, where
A
E
>
E
C
AE> EC
A
E
>
EC
. On the side
A
B
AB
A
B
, a different point from
B
B
B
has been selected for which
E
F
=
D
E
EF = DE
EF
=
D
E
. Prove that
∠
D
E
F
=
9
0
o
\angle DEF = 90^o
∠
D
EF
=
9
0
o
.
geometry
right angle
square