Đáp án:
B4:
b) A=-1
Giải thích các bước giải:
\(\begin{array}{l}
B4:\\
a)DK:x \ne \left\{ { - 6;0;6} \right\}\\
b)A = \left[ {\dfrac{{{x^2} - {{\left( {x - 6} \right)}^2}}}{{x\left( {x - 6} \right)\left( {x + 6} \right)}}} \right].\dfrac{{x\left( {x + 6} \right)}}{{2\left( {x - 3} \right)}} - \dfrac{x}{{x - 6}}\\
= \dfrac{{{x^2} - {x^2} + 12x - 36}}{{x\left( {x - 6} \right)\left( {x + 6} \right)}}.\dfrac{{x\left( {x + 6} \right)}}{{2\left( {x - 3} \right)}} - \dfrac{x}{{x - 6}}\\
= \dfrac{{12\left( {x - 3} \right)}}{{x\left( {x - 6} \right)\left( {x + 6} \right)}}.\dfrac{{x\left( {x + 6} \right)}}{{2\left( {x - 3} \right)}} - \dfrac{x}{{x - 6}}\\
= \dfrac{6}{{x - 6}} - \dfrac{x}{{x - 6}} = \dfrac{{6 - x}}{{x - 6}} = - 1
\end{array}\)
