cos^2(5pi/6 - x) = cos^2(5pi/6 + x)
(cos(5pi/6 – x) - cos(5pi/6 + x))*(cos(5pi/6 – x) - cos(5pi/6 + x))=0
Применяем формулы:
cos α -cos β =
cos α +cos β=
-2sin(-2x)*cos(10π/6) * 2*cos(10π/6)*cos(-2x)=0
sin(-2x)=-sin2x
cos(-2x)=cos2x
2sin2x*cos2x=sin4x
sin4x=0
4x=πk, k ∈ Z
[b]x=(π/4)k, k ∈ Z[/b]