<h3>cos(3x)•cos(π/4) + sin(3x)•sin(π/4) = - 0,5</h3>
cosα•cosβ + sinα•sinβ = cos(α - β)
<h3>cos(3x - (π/4)) = - 1/2</h3><h3>[ 3x - (π/4) = (2π/3) + 2πn ⇔ 3x = (11π/12) + 2πn ⇔ x = (11π/36) + (2πn/3) , n ∈ Z</h3><h3>[ 3x - (π/4) = (-2π/3) + 2πk ⇔ 3x = (-5π/12) + 2πk ⇔ x = (-5π/36) + (2πk/3) , k ∈ Z</h3><h3><u><em>ОТВЕТ: (11π/36) + (2πn/3), n ∈ Z ; (-5π/36) + (2πk/3), k ∈ Z</em></u></h3><h3><u><em /></u></h3>