4*(4cos^3x-3cosx)+3cosx=0
16cos^3x-12cosx+3cosx=0
16cos^3x-9cosx=0
cosx*(16cos^2x-9)=0
cosx=0 или 16cos^2x-9=0
cosx=0 ⇒x=(π/2)+πk, k∈Z
16cos^2x-9=0⇒
cosx=3/4 или сosx=-3/4
x=± arccos(3/4)+2πn, n∈Z или х=± (π)-arccos(3/4)+2πm, m∈Z
О т в е т. x=(π/2)+πk, ± arccos(3/4)+2πn,
± (π)-arccos(3/4)+2πm, k, n, m∈Z