Đáp án:
Giải thích các bước giải:
\(\begin{array}{l}
B12:\\
a.DK:x \ne \pm 2\\
A = \left( {\frac{{x - 2\left( {x + 2} \right) + x - 2}}{{\left( {x - 2} \right)\left( {x + 2} \right)}}} \right):\left( {\frac{{{x^2} - 4 + 10 - {x^2}}}{{x + 2}}} \right)\\
= \frac{{ - 6}}{{\left( {x - 2} \right)\left( {x + 2} \right)}}.\frac{{x + 2}}{6}\\
= \frac{{ - 1}}{{x - 2}}\\
b.\left| x \right| = \frac{1}{2}\\
\to \left[ \begin{array}{l}
x = \frac{1}{2}\\
x = - \frac{1}{2}
\end{array} \right.\\
\to \left[ \begin{array}{l}
A = \frac{2}{3}\\
A = \frac{2}{5}
\end{array} \right.
\end{array}\)
