Cos2a + 2sin (a+π/6) sin (a-π/6)

Cos2a+2 (sina*cos (п/6) + cosa*sin (п/6) * (sina*cos (п/6) - cosa*sin (п/6)) = cos2a+2 (sin^2 (a) * cos^2 (п/6) - cos^2 (a) * sin^2 (п/6)) = cos2a+2 (0.75*sin^2 (a) - 0.25*cos^2 (a)) = cos^2 (a) - sin^2 (a) + 1.5*sin^2 (a) - 0.5*cos^2 (a) = 0.5 (sin^2 (a) + cos^2 (a)) = 0.5 как то так)