\(\text{Đ}K:cosx\ne0\Leftrightarrow x\ne\frac{\pi}{2}+k\pi\)
\(Pt\Leftrightarrow\frac{4sinx}{cosx}+\frac{6cosx}{cosx}=\frac{1}{cos^2x}\\ \Leftrightarrow4tanx+6=tan^2x+1\\ \Leftrightarrow\left[{}\begin{matrix}tanx=-1\\tanx=5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\frac{3\pi}{4}+k\pi\\x=arctan5+k\pi\end{matrix}\right.\)