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Problem
Problem
With usual notations, if in a
Δ
A
B
C
\Delta ABC
Δ
A
B
C
,
b
+
c
11
=
c
+
a
12
=
a
+
b
13
\frac{b+c}{11} = \frac{c+a}{12} = \frac{a+b}{13}
11
b
+
c
=
12
c
+
a
=
13
a
+
b
, then prove that
cos
A
7
=
cos
B
19
=
cos
C
25
\frac{\cos A}{7} = \frac{\cos B}{19} = \frac{\cos C}{25}
7
cos
A
=
19
cos
B
=
25
cos
C
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