一道计算题的简算方法？

1/2005-1=-2004/2005
1/2004-1=-2003/2004
.....
1/1001-1=-1000/1001
1/1000-1=-999/1000

(-2004/2005)*(-2003/2004)*......*(-1000/1001)*(-999/1000)
=999/2005

共有1006个数相乘~所以可以把所有括号中的顺序反过来~~

(1-1/2005)(1-1/2004)(1-1/2003)........(1-1/1001)(1-1/1000)
=(2004/2005)(2003/2004)....(1000/1001)(999/1000)
=999/2005