Đáp án:
$\begin{array}{l}
a)2\left( {x - 4} \right) - 9\sqrt {16{{\left( {2x - 3} \right)}^2}} \left( {x \le \dfrac{3}{2}} \right)\\
= 2x - 8 - 9.4.\left| {2x - 3} \right|\\
= 2x - 8 - 36.\left( {3 - 2x} \right)\left( {do:x \le \dfrac{3}{2}} \right)\\
= 2x - 8 - 108 + 72x\\
= 74x - 116\\
b)\dfrac{{\sqrt {125{x^4}{y^8}} }}{{\sqrt {5{x^6}{y^6}} }}\left( {y < 0;x > 0} \right)\\
= \dfrac{{5\sqrt 5 .{x^2}{y^4}}}{{\sqrt 5 .\left| {{x^3}} \right|.\left| {{y^3}} \right|}}\\
= \dfrac{{5.{x^2}{y^4}}}{{{x^3}.{{\left( { - y} \right)}^3}}}\\
= \dfrac{{ - 5y}}{x}
\end{array}$
