Đáp án:
\(\dfrac{{ - 136y - 800}}{{\left( {4y + 24} \right)\left( {4y + 8} \right)}}\)
Giải thích các bước giải:
\(\begin{array}{l}
Do:x - y = 8\\
\to x = y + 8\\
Thay:x = y + 8\\
\to B = \dfrac{{4\left( {y + 8} \right) - 9}}{{3\left( {y + 8} \right) + y}} - \dfrac{{4\left( {y + 8} \right) + 9}}{{3y + y + 8}}\\
= \dfrac{{4y + 23}}{{4y + 24}} - \dfrac{{4y + 41}}{{4y + 8}}\\
= \dfrac{{\left( {4y + 23} \right)\left( {4y + 8} \right) - \left( {4y + 41} \right)\left( {4y + 24} \right)}}{{\left( {4y + 24} \right)\left( {4y + 8} \right)}}\\
= \dfrac{{16{y^2} + 124y + 184 - 16{y^2} - 260y - 984}}{{\left( {4y + 24} \right)\left( {4y + 8} \right)}}\\
= \dfrac{{ - 136y - 800}}{{\left( {4y + 24} \right)\left( {4y + 8} \right)}}
\end{array}\)
