Đáp án:
$\begin{array}{l}
4)T = \dfrac{{1 - \cos \dfrac{x}{2}}}{{1 + \cos \dfrac{x}{2}}} = \dfrac{{2{{\sin }^2}\dfrac{x}{4}}}{{2{{\cos }^2}\dfrac{x}{4}}}\\
= {\tan ^2}\dfrac{x}{4} = {\cot ^2}\left( {\dfrac{x}{4} + \dfrac{\pi }{4}} \right) = {\cot ^2}\left( {\dfrac{{x + \pi }}{4}} \right)\\
\Rightarrow B\\
5)y = \dfrac{{1 + \cos 2x + \sin 2x}}{{1 - \cos 2x + \sin 2x}}\\
= \dfrac{{2{{\cos }^2}x + 2.cosx.sinx}}{{2{{\sin }^2}x + 2\sin x.\cos x}}\\
= \dfrac{{2\cos x\left( {\cos x + \sin x} \right)}}{{2\sin x\left( {\sin x + \cos x} \right)}}\\
= \dfrac{{2\cos x}}{{2\sin x}} = \cot x\\
\Rightarrow C
\end{array}$
