\( \frac{x(x-y)}{4y} \cdot \frac{y^{2}}{2x^{3}} = \frac{x(x-y)y^{2}}{4y \cdot 2x^{3}} = \frac{(x-y)y}{8x^{2}} \)
Ответ: $$\frac{y(x-y)}{8x^{2}}$$