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Problem
Problem
Show that,
4
R
r
cos
A
2
cos
B
2
cos
C
2
=
S
4Rr \cos \frac{A}{2} \cos \frac{B}{2} \cos \frac{C}{2} = S
4
R
r
cos
2
A
cos
2
B
cos
2
C
=
S
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