$ \begin{aligned}解:原式&=8x2 \sqrt{xy}÷\sqrt {\frac {x^{3} }{9y}}×(-\sqrt {\frac {y^{2} }{x}} ) \\ &=-8x2 \sqrt{xy·\frac{9y}{x^{3} }·\frac {y^{2} }{x}} \\ &=-8x2\sqrt {\frac {9y^{4} }{x^{3} }}\ \\ &=-8x2·\frac{3y2\sqrt{x}}{x2} \\ &=-24y2\sqrt{x}. \\ \end{aligned}$