$\begin{array}{l} A = 4\sqrt {\dfrac{{25x}}{4}} - \dfrac{8}{3}\sqrt {\dfrac{{9x}}{4}} - \dfrac{4}{{3x}}.\sqrt {\dfrac{{9{x^3}}}{{64}}} \\ A = 4.\sqrt {{{\left( {\dfrac{5}{2}} \right)}^2}x} - \dfrac{8}{3}.\sqrt {{{\left( {\dfrac{3}{2}} \right)}^2}.x} - \dfrac{4}{{3x}}.\sqrt {{{\left( {\dfrac{{3x}}{8}} \right)}^2}.x} \\ A = 4.\dfrac{5}{2}.\sqrt x - \dfrac{8}{3}.\dfrac{3}{2}.\sqrt x - \dfrac{4}{{3x}}.\dfrac{{3\left| x \right|}}{8}.\sqrt x \\ A = 10\sqrt x - 4\sqrt x + \dfrac{1}{2}\sqrt x = \dfrac{{13}}{2}\sqrt x \left( {do\,x > 0} \right)\\ B = \dfrac{y}{2} + \dfrac{3}{4}\sqrt {1 - 4y + 4{y^2}} - \dfrac{3}{2}\\ B = \dfrac{y}{2} + \dfrac{3}{4}\sqrt {{{\left( {2y - 1} \right)}^2}} - \dfrac{3}{2}\\ B = \dfrac{y}{2} + \dfrac{{3\left( {1 - 2y} \right)}}{4} - \dfrac{3}{2}\left( {y \le \dfrac{1}{2} \Rightarrow 2y - 1 < 0} \right)\\ B = \dfrac{y}{2} + \dfrac{3}{4} - \dfrac{{3y}}{2} - \dfrac{3}{2} = - y - \dfrac{3}{4} \end{array}$
