原式= 1 x+1 - x+3 (x+1)(x?1) ? (x?1)2 (x+1)(x+3) = 1 x+1 - x?1 (x+1) 2 = x+1?(x?1) (x+1)2 = 2 (x+1)2 ,∵x= 17 3 2 +1 = 17(3 2 ?1) (3 2 +1)(3 2 ?1) =3 2 -1,∴原式= 2 (3