Show that the sum of the residuals is zero?

false, adding a number to 0 like 0+9 would =9. only when you multiply 0 by a number is the answer 0.

Any negative number.

Yes because it is like adding nothing.

Think about it like this. 0+x would equal x+0 but if you did the opposite then the answer would still equal x+0 because 'x' is an indefinite number and if you times, divide, subtract or plus then it...

The sum of 0 and 1 is 1. 0+1=1If you have 1, and you add 0(which is nothing), then you will still have 1.