6cos^2(x)+11cos(x) +4=0

6cos²x+11cos x+4 = 0cos x = t, cos²x = t², t∈[-1; 1]6t²+11t+4 = 0D = 121-4*6*4 = 25t1 = (-11-5)/12 = -1 1/3 - не подходит.t2 = (-11+5)/12 = -1/2cos x = 1/2x = ±2π/3+2πn, n∈Z