Đáp án:
$\begin{array}{l}
\tan x = 0,5 = \dfrac{1}{2} = \dfrac{{\sin x}}{{\cos x}}\\
\Leftrightarrow \cos x = 2\sin x\\
A = \dfrac{{\cos x + 3\sin x}}{{\sin x - 2\cos x}}\\
= \dfrac{{2\sin x + 3\sin x}}{{\sin x - 2.2\sin x}}\\
= \dfrac{{5\sin x}}{{ - 3\sin x}} = \\
= - \dfrac{5}{3}\\
B = \dfrac{{{{\cos }^3}x - 2{{\sin }^3}x}}{{{{\sin }^3}x + {{\cos }^3}x}}\\
= \dfrac{{{{\left( {2\sin x} \right)}^3} - 2{{\sin }^3}x}}{{{{\sin }^3}x + {{\left( {2\sin x} \right)}^3}}}\\
= \dfrac{{6{{\sin }^3}x}}{{9{{\sin }^3}x}}\\
= \dfrac{2}{3}
\end{array}$
