`~rai~`
\(a)\dfrac{2}{x^2-y^2}\sqrt{\dfrac{3(x+y)^2}{2}}\quad(x\ge0;y\ge0;x\ne y)\\=\dfrac{2}{x^2-y^2}.\sqrt{(x+y)^2}.\sqrt{\dfrac{3}{2}}\\=\dfrac{2.|x+y|}{x^2-y^2}.\dfrac{\sqrt{3}}{\sqrt{2}}\\=\dfrac{2(x+y)}{(x+y)(x-y)}.\dfrac{\sqrt{6}}{2}\quad\text{(vì x}\ge0;y\ge0)\\=\dfrac{2}{x-y}.\dfrac{\sqrt{6}}{2}\\=\dfrac{\sqrt{6}}{x-y}.\\b)\dfrac{2}{2a-1}\sqrt{5a^2(1-4a+4a^2)}\quad(a>0,5)\\=\dfrac{2}{2a-1}.\sqrt{1-4a+4a^2}.\sqrt{5a^2}\\=\dfrac{2}{2a-1}.\sqrt{(1-2a)^2}.|a|\sqrt{5}\\=\dfrac{2}{2a-1}.|2a-1|.|a|\sqrt{5}\\=\dfrac{2}{2a-1}.(2a-1).a\sqrt{5}\quad\text{(vì a>0,5)}\\=2.a\sqrt{5}=2a\sqrt{5}.\)
