The 2012 was just put in there to complicate matters. It could have been any number whatever. Most likely this problem was made up 5 years ago in in 2012. Let's just divide everything through by 2012:, , and Add all those equations together: Multiply thru by 2012: So We want to compute: Substitute -x-y for z Edwin 
x = 2012(a - b), y = 2012(b - c), and z = 2012(c - a) ===> x + y + z = 2012*(a-b+b-c+c-a) = 0. Hence 0 == = + ===> = ===> = -2.