Giải thích các bước giải:
\(\begin{array}{l}
2)\,a)\,A = \dfrac{{xy\left( {3y - x} \right)}}{{xy\left( {x - y} \right)}} - \dfrac{{xy\left( {3x - y} \right)}}{{xy\left( {x - y} \right)}}\\
= \dfrac{{3y - x - 3x + y}}{{x - y}} = \dfrac{{4y - 4x}}{{x - y}} = \dfrac{{ - 4\left( {x - y} \right)}}{{x - y}} = - 4\\
b)\,B = \dfrac{x}{{\left( {x - 2} \right)\left( {x - 3} \right)}} + \dfrac{2}{{x - 2}} + \dfrac{x}{{x - 3}}\\
= \dfrac{{x + 2\left( {x - 3} \right) + x\left( {x - 2} \right)}}{{\left( {x - 2} \right)\left( {x - 3} \right)}}\\
= \dfrac{{3x - 6 + x\left( {x - 2} \right)}}{{\left( {x - 2} \right)\left( {x - 3} \right)}}\\
= \dfrac{{3\left( {x - 2} \right) + x\left( {x - 2} \right)}}{{\left( {x - 2} \right)\left( {x - 3} \right)}}\\
= \dfrac{{\left( {x + 3} \right)\left( {x - 2} \right)}}{{\left( {x - 2} \right)\left( {x - 3} \right)}}\\
= \dfrac{{x + 3}}{{x - 3}}
\end{array}\)
