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Mathematics
Mathematics
Problem
If
3
tan
A
tan
B
=
1
3 \tan A \tan B = 1
3
tan
A
tan
B
=
1
, then prove that
cos
(
A
−
B
)
cos
(
A
+
B
)
=
2
\frac{\cos(A-B)}{\cos(A+B)} = 2
c
o
s
(
A
+
B
)
c
o
s
(
A
−
B
)
=
2
.
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