Final answer:
When a point is reflected across the y-axis, the x-coordinate changes sign, but the y-coordinate remains the same.
Step-by-step explanation:
When a point is reflected across the y-axis, the x-coordinate changes sign, but the y-coordinate remains the same.
Let's say the coordinates of point A are (x, y). When reflected across the y-axis, the x-coordinate becomes -x. Therefore, the coordinates of point A' are (-x, y).
In the case of a rectangle, the vertex A is one of the corners of the rectangle. So, if the coordinates of point A are (x1, y1), the coordinates of the reflected point A' will be (-x1, y1).