Applying the distributive property when distributing a negative 1.

We started substitution for systems of equations today and the major hangup for students was the distribution of -1.  My CT had a turn of phrase he applied to this situation intended to guide students through the distribution.  He offered the strategy of thinking of a minus sign as meaning “Take the opposite of.”  Let’s say you are substituting the y value of (-x +2) into 2x – y = 5, resulting in the equation 2x – (-x +2) = 5. This is his turn of phrase which applies the “opposite” approach; “Think of the negative in front of the paenthesis as ‘the opposite’.  So ‘the opposite’ of negative x is positve x, ‘the opposite’ of positive 2 is negative 2.”  This should yeild 2x +x -2 = 5.  It is much smoother when you actually hear it said while watching him actually figure it on the doc cam.