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Mathematics
Problem
A re-entrant (concave) quadrilateral
A
B
C
D
ABCD
A
B
C
D
resembles a dart. The vertex
D
D
D
is inside the
△
A
B
C
\triangle ABC
△
A
B
C
. If
A
B
=
A
C
=
10
cm
AB = AC = 10\,\text{cm}
A
B
=
A
C
=
10
cm
,
∠
B
A
C
=
60
∘
\angle BAC = 60^{\circ}
∠
B
A
C
=
6
0
∘
, and
D
D
D
is the exact center of the equilateral
△
A
B
C
\triangle ABC
△
A
B
C
, find the area of the quadrilateral
A
B
D
C
ABDC
A
B
D
C
.
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