Let f(x)=(cos(2x8))(sin(2x+4))\displaystyle {f{{\left({x}\right)}}}={\left({\cos{{\left({2}{x}-{8}\right)}}}\right)}{\left({\sin{{\left(-{2}{x}+{4}\right)}}}\right)}.

Then f(x)=\displaystyle {f}'{\left({x}\right)}=