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Mathematics
Mathematics
Problem
In any
Δ
A
B
C
\Delta ABC
Δ
A
B
C
,
2
[
b
c
cos
A
+
c
a
cos
B
+
a
b
cos
C
]
=
2[bc \cos A + ca \cos B + ab \cos C] =
2
[
b
c
cos
A
+
c
a
cos
B
+
ab
cos
C
]
=
a.
a
2
+
b
2
+
c
2
a^2 + b^2 + c^2
a
2
+
b
2
+
c
2
b.
a
2
+
b
2
−
c
2
a^2 + b^2 - c^2
a
2
+
b
2
−
c
2
c.
a
2
−
b
2
+
c
2
a^2 - b^2 + c^2
a
2
−
b
2
+
c
2
d. None of these
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