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Điều kiện $\cos x \ne 0.$
PT
$\Leftrightarrow \sin x +\dfrac{\sin x}{\cos x} =\dfrac{1-\cos^2x}{\cos x} $
$\Leftrightarrow \dfrac{\sin x(1+\cos x)}{\cos x} =\dfrac{\sin^2 x}{\cos x} $
$\Leftrightarrow \left[ {\begin{matrix} \sin x=0\\ 1+\cos x=\sin x \end{matrix}} \right. $
$\Leftrightarrow \left[ {\begin{matrix} \sin x=0\\ \sin x-\cos x=-1 \end{matrix}} \right. $
$\Leftrightarrow \left[ {\begin{matrix} \sin x=0\\ \sin( x-\dfrac{\pi}{4})=-1/\sqrt 2 \end{matrix}} \right. $
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