\(\left(x-2y\right)\sqrt{\frac{xy}{\left(x-2y\right)^2}}\)(x<2y<0)
\(=\left(x-2y\right)\frac{\sqrt{xy}}{\sqrt{\left(x-2y\right)^2}}=\left(x-2y\right)\frac{\sqrt{xy}}{\left|x-2y\right|}=\left(x-2y\right)\frac{\sqrt{xy}}{-\left(x-2y\right)}\)
\(=-\sqrt{xy}\)