Cos^2x+5cosx-6=0 помогите решить

[latex]\cos^2x+5\cos x-6 = 0\\ (\cos x+6)(\cos x-1) = 0\\ \left [ {{\cos x=-6} \atop {\cos x=1}} \right. \\ \cos x = 1\\ x = 2\pi k, k\in\mathbb{Z}[/latex]