When a reflection occurs, the original graph and the reflected graph are mirror images of each other. So, when the graph is reflected about the y-axis, think of the y-axis as the mirror. When you fold the graph length-wise, you will see that both graphs would coincide. Thus, their y-coordinate would not change. It would only change to the opposite quadrant, thereby changing the signs of the x-coordinates. So, as a rule, during reflection, the coordinates (x,y) is changed to (-x,y).
Therefore, the answer is:The x-coordinates' signs change..
