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Problem
Problem
In a
Δ
A
B
C
\Delta ABC
Δ
A
B
C
, show that
a
cos
A
+
b
cos
B
+
c
cos
C
a
+
b
+
c
=
r
R
\frac{a \cos A + b \cos B + c \cos C}{a + b + c} = \frac{r}{R}
a
+
b
+
c
a
c
o
s
A
+
b
c
o
s
B
+
c
c
o
s
C
=
R
r
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