（1998/1-1）（1997/1-1）（1996/1-1).（1001/1-1）（1000/1-1）.

（1998/1-1）（1997/1-1）（1996/1-1).（1001/1-1）（1000/1-1）.

From 1000 to 1998, it is easy to know that there are 999 items in total, then the negative items are odd, and the product is negative. The original formula = (1 - 1 / 1998) (1 - 1 / 1997) (1 - 1/1000)= - 1997/1998 × 1996/1997 × …… ×999/1000= - 999/1998=...

（1998/1-1）*（1997/1-1）*（1996/1-1)*.*（1001/1-1）*（1000/1-1）.

（1998/1-1）*（1997/1-1）*（1996/1-1)*.*（1001/1-1）*（1000/1-1）=(-1997/1998)*(-1996/1997)*(-1995/1995)*…… *(- 999 / 1000) has a total of 1998-1000 + 1 = 999 negative numbers multiplied, so the product is still negative. The molecule of the first fraction can be multiplied with the latter fraction