Вычислите cos26°cos22°−cos64°cos 68°/2 sin 21° cos 21° с решением, : )

(cos26cos22-cos64cos68)/(2sin21cos21)=
cos64=cos(90-26)=sin26
cos68=cos(90-22)=sin22

(cos26cos22-sin26sin22)/(2sin21cos21)=cos(26+22)/(sin(2*21))=2cos48/sin42=
=cos48/sin(90-42)=cos48/cos48=1