I am not sure whether this is worth a question or I am just forgetting something, but Mathematica does not simplify the Cos^2+Sin^2 for me on Mathematica 13, Ubuntu 20.04
'FullSimplify[
Simplify[-(1/4) (Cos[\[Gamma]1]^2 + Sin[\[Gamma]1]^2) (-4 + x1^2 +
x2^2 + x3^2 + x4^2)]]'
Can somebody confirm that? Maybe even explain why?