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Problem
Problem
In any
Δ
A
B
C
\Delta ABC
Δ
A
B
C
,
(
b
−
c
a
)
cos
2
(
A
2
)
+
(
c
−
a
b
)
cos
2
(
B
2
)
+
(
a
−
b
c
)
cos
2
(
C
2
)
\left(\frac{b-c}{a}\right) \cos^2 \left(\frac{A}{2}\right) + \left(\frac{c-a}{b}\right) \cos^2 \left(\frac{B}{2}\right) + \left(\frac{a-b}{c}\right) \cos^2 \left(\frac{C}{2}\right)
(
a
b
−
c
)
cos
2
(
2
A
)
+
(
b
c
−
a
)
cos
2
(
2
B
)
+
(
c
a
−
b
)
cos
2
(
2
C
)
is equal to a.
b
2
−
c
2
a
2
\frac{b^2 - c^2}{a^2}
a
2
b
2
−
c
2
b.
c
2
−
a
2
b
2
\frac{c^2 - a^2}{b^2}
b
2
c
2
−
a
2
c.
a
2
−
b
2
c
2
\frac{a^2 - b^2}{c^2}
c
2
a
2
−
b
2
d. 0
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