Ответы на вопрос:
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
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