Преобразовать в произведение:

cos (a) + sin (a) - cos2 (pi)

cos (α) + sin (α) - cos (2π);

1) cos (α) - cos (2π) = - 2sin ((α+2π) / 2) sin ((α-2π) / 2) = - 2sin (α/2+π) sin (α/2-π) =

=2sin (π+α/2) sin (π-α/2) = - 2sin (α/2) sin (α/2);

2) sin (α) = 2sin (α/2) cos (α/2);

1+2) 2sin (α/2) cos (α/2) - 2sin (α/2) sin (α/2) = 2sin (α/2) (cos (α/2) - sin (α/2));