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Problem
Problem
In a
Δ
A
B
C
\Delta ABC
Δ
A
B
C
,
b
c
cos
2
A
2
+
c
a
cos
2
B
2
+
a
b
cos
2
C
2
bc \cos^2 \frac{A}{2} + ca \cos^2 \frac{B}{2} + ab \cos^2 \frac{C}{2}
b
c
cos
2
2
A
+
c
a
cos
2
2
B
+
ab
cos
2
2
C
is equal to a.
(
s
−
a
)
2
(s-a)^2
(
s
−
a
)
2
b.
(
s
−
b
)
2
(s-b)^2
(
s
−
b
)
2
c.
(
s
−
c
)
2
(s-c)^2
(
s
−
c
)
2
d.
s
2
s^2
s
2
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