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Mathematics
Problem
Prove that for every real
x
x
x
for which
tan
x
\tan x
tan
x
is defined,
tan
2
x
=
2
tan
x
1
−
tan
2
x
.
\tan 2x = \frac{2\tan x}{1-\tan^{2}x}.
tan
2
x
=
1
−
tan
2
x
2
tan
x
.
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