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Mathematics
Mathematics
Problem
Using vector method, prove that in a triangle,
a
2
=
b
2
+
c
2
−
2
b
c
cos
A
a^2 = b^2 + c^2 - 2bc \cos A
a
2
=
b
2
+
c
2
−
2
b
c
cos
A
(cosine law).
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