2 câu trả lời
$VT=\dfrac{\sin^2x}{\cos^2x}-\sin^2x$
$\dfrac{\sin^2x-\sin^2x.\cos^2x}{\cos^2x}$
$=\dfrac{\sin^2x(1-\cos^2x)}{\cos^2x}$
$=\dfrac{\sin^2x.\sin^2x}{\cos^2x}$
$=\tan^2x.\sin^2x$
$= VP$
$VT=\dfrac{\sin^2x}{\cos^2x}-\sin^2x$
$\dfrac{\sin^2x-\sin^2x.\cos^2x}{\cos^2x}$
$=\dfrac{\sin^2x(1-\cos^2x)}{\cos^2x}$
$=\dfrac{\sin^2x.\sin^2x}{\cos^2x}$
$=\tan^2x.\sin^2x$
$= VP$
