原式=（ x+y x2?y2 + x?y x2?y2 ）÷ x2y x2?y2 = 2x x2y = 2 xy ，当x＝ 3 +1，y＝ 3 ?1时，原式= 2 xy = 2 ( 3 +1)( 3 ?1) = 2 3?1 =1．
