The root sign and mean square deviation are greater than or equal to 0.

The sum is equal to 0, one is greater than 0 and the other is less than 0, which is not true.

So both are equal to 0.

So a- 1=0 and ab-2=0.

a= 1，b=2/a=2

So the original formula =11* 2+1/2 * 3+...+1/2005 * 2006.

= 1- 1/2+ 1/2- 1/3+ 1/3- 1/4+……+ 1/2006- 1/2006

= 1- 1/2006

=2005/2006