1\;-\;HE\;nogx.\\\cos x=-1\\x=\pi+2\pi n,\;n\in\mathbb{Z}" alt="8\sin^2x+\cos x+1=0\\8(1-\cos^2x)+\cos x+1=0\\8\cos^2x+\cos x+1=0\\\cos^2x-\cos x-9=0\\\cos x=t,\;\cos^2x=t^2,\;t\in[-1;\;1]\\8t^2-t-9=0\\D=1+4\cdot8\cdot9=1+288=289=(17)^2\\t_1=\frac{1-17}{16}=-1\\t_2=\frac{1+17}{16}=\frac{18}{16}>1\;-\;HE\;nogx.\\\cos x=-1\\x=\pi+2\pi n,\;n\in\mathbb{Z}" align="absmiddle" class="latex-formula">