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Mathematics
Problem
A cyclic quadrilateral
A
B
C
D
ABCD
A
B
C
D
has side lengths
A
B
=
4
AB = 4
A
B
=
4
,
B
C
=
5
BC = 5
B
C
=
5
,
C
D
=
6
CD = 6
C
D
=
6
, and
D
A
=
7
DA = 7
D
A
=
7
. Find the cosine of
∠
B
\angle B
∠
B
.
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