sin2A-cos2A= 2cos2Atan@A-1

You identity formula is incorrect. Not sure whether you meant this:


\sin (2A) - \cos (2A) = 2 \cos (2A) tan(A) - 1


or this:


\sin (2A) - \cos (2A) = 2 \cos (2A) tan(2A) - 1


But neither of these formulas is correct.