Tính các hiệu sau 1 / (2x - 3) - 13 / ((2x - 3) (4x + 7))

\(\frac{1}{{2x - 3}} - \frac{{13}}{{\left( {2x - 3} \right)\left( {4x + 7} \right)}}\)

= \(\frac{{4x + 7}}{{\left( {2x - 3} \right)\left( {4x + 7} \right)}} - \frac{{13}}{{\left( {2x - 3} \right)\left( {4x + 7} \right)}}\) (Mẫu thức chung là: (2x – 3)(4x + 7))

= \(\frac{{4x + 7 - 13}}{{\left( {2x - 3} \right)\left( {4x + 7} \right)}}\)

= \(\frac{{4x - 6}}{{\left( {2x - 3} \right)\left( {4x + 7} \right)}}\)

= \(\frac{{2\left( {2x - 3} \right)}}{{\left( {2x - 3} \right)\left( {4x + 7} \right)}}\)

= \(\frac{2}{{4x + 7}}\).