Respuesta :

arthurpdc
[tex]
\cos^2(x)+2\cos(x)+1=0\\\\
(\cos(x)+1)^2=0\\\\
\text{So:}\\\\
\cos(x)+1=0\\\\
\cos(x)=-1\\\\
\boxed{x=\pi+2k\pi},~k\in\mathbb{Z}[/tex]
Hope this helps you.
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