Final answer:
The property of equality represented by the equation x - a = y - a when x = y is the addition property of equality.
Step-by-step explanation:
The property of equality represented by the equation x - a = y - a when x = y is the addition property of equality.
This property states that if you add or subtract the same quantity from both sides of an equation, the resulting expression will still be true.
In this case, subtracting 'a' from both sides of the equation keeps the equality between x and y intact, as the same quantity has been subtracted on both sides.