@JimB I know that TrigReduce and TrigExpand work. However, this is a small part of a ginormous expression to which I can't apply either, because then the whole expression becomes orders of magnitude larger and Mathematica takes ages to do anything with it, but I don't want to have to go through the expression and replace every occurrence of a trigonometric identity by hand.
in particular, it will be interesting whether executing that code in different versions of Mathematica always leaves Cos^2+SIn^2 like that
@ThunderBiggi Maybe it's a bug. It appears that, if Simplify is added to the transformation functions, it's reduced to 1 but that simplification is rejected. No idea why. Code:
@MichaelE2 That is interesting. Can somebody check in older version of Mathematica (I am using 13)
Because I don't remember encoutering such terms before in my calcualtions (and I have been doing more or less the same type of stuff for years with Mathematica)