if the problem is
[sqrt(1 - {cot(x) * cot(x)}) * sqrt(1 - {tan(x) * tan(x)})] / cos(x) = tan(2x)
and the angles are real numbers,
then it is NOT an identity. in fact, it is NEVER true, which would make it an ANTI-IDENTITY, i suppose.
nice try though
(for those interested - plug in a few angles to see what happens)