Шаг 1: Упростим выражение.
$$rac{xy(x^2-y^2)}{2(y-x)} imes rac{3(x-y)}{x^2-y^2} = rac{xy}{2(y-x)} imes 3(x-y) = rac{xy}{2(-(x-y))} imes 3(x-y) = -rac{3xy}{2}$$
Шаг 2: Подставим значения x и y.
$$-rac{3 imes 4 imes rac{1}{4}}{2} = -rac{3}{2}$$