Cos12x = Cos²6x - Sin²6x = (Cos6x - Sin6x)(Cos6x + Sin6x)
(Cos6x + Sin6x)(Cos6x - Sin6x - 1)=0
1) Cos6x + Sin6x = 0 ⇔ tg6x = -1
6x = 3π/4 + πn, n∈Z
x = π/8 + πn/6, n∈Z
2) Cos6x - Sin6x - 1 = 0
Cos6x - Sin6x = √2(Cos6x*Cos(π/4) - Sin6x*Sin(π/4))=√2Cos(6x + π/4)
√2Cos(6x + π/4) = 1
Cos(6x + π/4) = √2/2
6x + π/4 = ±π/4 + 2πn, n∈Z
x = πn/3 и x = -π/12 + πn/3, n∈Z
