2sin(α)cos(п/2-α)-2cos(-α)sin(п/2-α)
cos((π/2)- α )=sin α
sin((π/2)- α )=cos α
Так как косинус - четная функция
cos(- α )=cos α
2sin α *cos((π/2)- α )-2cos(- α )*sin((π/2)- α )=
=2sin α *sin α -2cos α *cos α =
=2sin^2 α -2cos^2 α =
= -2*(cos^2 α -sin^2 α )=
=-2cos2 α