Each cell of a 1997x1997 square grid contains either +1 or -1, with no cell being vacant.

The product of all the numbers in the ith row, and the product of all the numbers in the ith column are respectively denoted by R_i and C_i.

               1997
Prove that  Σ_i=1(R_i + C_i) is always nonzero.

(In reply to re: Solution - (MS Word Formatting!?) by farcear)

It's best to use a text editor, such as Notepad, rather than a word processor, such as Word. 

word processors have much embedded, invisible formatting stuff that gets carried over, not conducive to any method of entry in the comments.

Posted by Charlie on 2010-04-30 02:17:37