$ \begin{aligned}解:原式&= \frac{3x+y-2x}{x2-y2}·\frac {xy(x-y)}{2} \\ &=\frac{x+y}{(x+y)(x-y)}· \frac{xy(x-y)}{2} \\ &= \frac{xy}{2} ， \\ \end{aligned}$
$當(dāng)x= \sqrt{3} +1，y= \sqrt{3} 時(shí)，$
$ \begin{aligned}原式&= \frac{(\sqrt {3} +1)×\sqrt{3}}{2} \\ &= \frac{3+\sqrt{3}}{2}. \\ \end{aligned}$
