1.
\(\Leftrightarrow3\left(2cos^22x-1\right)-\left(1-cos^22x\right)+cos2x-2=0\)
\(\Leftrightarrow7cos^22x+cos2x-6=0\)
\(\Leftrightarrow\left[{}\begin{matrix}cos2x=-1\\cos2x=\frac{6}{7}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{\pi}{2}+k\pi\\x=\pm\frac{1}{2}arccos\left(\frac{6}{7}\right)+k\pi\end{matrix}\right.\)
2.
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\(\Leftrightarrow1+cot^2x+3cotx+1=0\)
\(\Leftrightarrow cot^2x+3cotx+2=0\)
\(\Leftrightarrow\left[{}\begin{matrix}cotx=-1\\cotx=-2\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-\frac{\pi}{4}+k\pi\\x=arccot\left(-2\right)+k\pi\end{matrix}\right.\)
3.
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\(\sqrt{3}tanx+\frac{1}{tanx}-\sqrt{3}-1=0\)
\(\Leftrightarrow\sqrt{3}tan^2x-\left(\sqrt{3}+1\right)tanx+1=0\)
\(\Leftrightarrow\left[{}\begin{matrix}tanx=1\\tanx=\frac{1}{\sqrt{3}}\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\frac{\pi}{4}+k\pi\\x=\frac{\pi}{6}+k\pi\end{matrix}\right.\)
4.
\(\Leftrightarrow2cos^2x-1-3cosx=2+2cosx\)
\(\Leftrightarrow2cos^2x-5cosx-3=0\)
\(\Leftrightarrow\left[{}\begin{matrix}cosx=-\frac{1}{2}\\cosx=3>1\left(l\right)\end{matrix}\right.\)
\(\Rightarrow x=\pm\frac{2\pi}{3}+k2\pi\)