Trigonometric reduction formulas

[Nigel (UK)]

(03-23-2020 03:47 PM)parisse Wrote:  cot is not a fundemental trigonometric function inside the CAS, it will always be rewritten with sin and cos.
You can run e.g. sincos(tan(pi/2-x)) if you want to remove a pi/2-multiple phase shift in a tan function.

I'm not asking for cot to be given as an answer. It just seems strange that texpand acting on \(\tan(a-b)\) returns \((\tan a -\tan b)/(1+\tan a\tan b)\), but acting on \(\tan((\pi/2)-b)\) texpand returns "undef". This expression is perfectly well-defined. Returning either \(\cos x/\sin x\), \(1/\tan x\), or even the original expression unchanged would be better than "undef".

I appreciate that it is not possible for a CAS - especially on a calculator - to consider every special case in every situation, so I do understand if things are left as they are.

Nigel (UK)