а) y^3 + 3y = y * (y^2 + 3)
1)Cos (п+а)*Sin (-2a) /2ctg (1,5π-a) = CosαSin2α/tgα =
= Cosα*2SinαCosα: Sinα/Cosα = Cosα*2SinαCosα * Cosα/Sinα= 2Cos³α
2) 2Cos2a/(1-Sina) +2Cos (0,5π+a) = 2(1 - 2Sin²α)/(1 - Sinα) - 2Sinα =
= (2 - 4Sin²α - 2Sinα + 2Sin²α)/(1 - Sinα) = (2 - 2Sinα - 2Sin²α)/(1 - Sinα)
Cos²x - 1/2sin2x + cosx = sinx
cos²x - 1/2·2sinxcosx + cosx - sinx = 0
cos²x - sinxcosx + cosx - sinx = 0
cosx(cosx - sinx) + (cosx - sinx) = 0
(cosx + 1)(cosx - sinx) = 0
1) cosx + 1 = 0
cosx = -1
x = π + 2πn, n ∈ Z
2) cosx - sinx = 0
sinx = cosx
tgx = 1
x = π/4 + πk, k ∈ Z
Ответ: x = π + 2πn, n ∈ Z; π/4 + πk, k ∈ Z.