(cosx - cos(1.5π + x)) / (2cos²x - sin2x) =
= (cosx - sinx) / (2cos²x - 2cosx·sinx) =
= (cosx - sinx) / (2cosx(cosx -sinx)) =
= 1/(2cosx)
(cosx - cos(1.5π + x)) / (2cos²x - sin2x) =
= (cosx - sinx) / (2cos²x - 2cosx·sinx) =
= (cosx - sinx) / (2cosx(cosx -sinx)) =
= 1/(2cosx)