Solution of a System. In general, a solution of a system in two variables is an ordered pair that makes BOTH equations true. In other words, it is where the two graphs intersect, what they have in common. So if an ordered pair is a solution to one equation, but not the other, then it is NOT a solution to the system.
The commutative property is a property of <em>addition</em>, not of <em>subtraction</em>. It can work in a subtraction problem if you keep the sign with the number, so you're adding positive and negative numbers.
