Giải thích các bước giải:
$2) a) VT=\dfrac{\cot x}{\cos x}-\dfrac{\cos x}{\tan x}\\
=\dfrac{\cot x.\tan x}{\cos x.\tan x}-\dfrac{\cos^2 x}{\tan x.\cos x }\\
=\dfrac{1-\cos^2x}{\dfrac{\sin x}{\cos x}.\cos x}\\
=\dfrac{\sin^2x}{\sin x}=\sin x=VP\Rightarrow ĐPCM\\
b)VT= (\sin \alpha+\tan \alpha).\dfrac{1}{1+\cos \alpha}\\
=(\sin \alpha+\dfrac{\sin \alpha}{\cos \alpha}).\dfrac{1}{1+\cos \alpha}\\
=\dfrac{\sin \alpha.\cos\alpha+\sin \alpha}{\cos \alpha}.\dfrac{1}{1+\cos \alpha}\\
=\dfrac{\sin \alpha.(\cos\alpha+1)}{\cos \alpha}.\dfrac{1}{1+\cos \alpha}\\
=\tan\alpha=VP\Rightarrow ĐPCM$
