Хелп плиз
Cos(4x+2x)+4cos2x>0 cos4x*cos2x-sin4x*sin2x+4cos2x>0 cos4x*cos2x-2sin²2x*cos2x+4cos2x>0 cos2x*(cos4x-2sin²2x+4)>0 cos2x*(2cos²2x-1-2+2cos²2x+4)>0 cos2x*(4cos²2x+1)>0 4cos²2x+1>0 при любом х⇒ cos2x>0 -π/2+πk<2x<π/2+πk<br>-π/4+πk/2<x<π/4+πk/2,k∈z