ĐKXĐ: x<>pi/2+kpi
\(\Leftrightarrow2:\left(\dfrac{sin^2x}{cos^2x}+1\right)-cosx-1=0\)
\(\Leftrightarrow2:\left(\dfrac{1-cos^2x+cos^2x}{cos^2x}\right)-cosx-1=0\)
\(\Leftrightarrow2cos^2x-cosx-1=0\)
\(\Leftrightarrow\left(cosx-1\right)\left(2cosx+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=k2pi\\x=\pm\dfrac{2}{3}pi+k2pi\end{matrix}\right.\)