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Problems
Problem
Problem
In a
Δ
A
B
C
\Delta ABC
Δ
A
B
C
,
a
2
cos
2
B
+
b
2
cos
2
A
+
2
a
b
cos
(
A
−
B
)
=
a^2 \cos 2B + b^2 \cos 2A + 2ab \cos(A - B) =
a
2
cos
2
B
+
b
2
cos
2
A
+
2
ab
cos
(
A
−
B
)
=
a.
a
2
a^2
a
2
b.
c
2
c^2
c
2
c.
b
2
b^2
b
2
d.
a
2
+
b
2
a^2 + b^2
a
2
+
b
2
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