Question

Polygon ABCD is drawn with vertices A(−4, −4), B(−4, −6), C(−1, −6), D(−1, −4). Determine the image coordinates of B′ if the preimage is reflected across y = 3.

B′(−4, 6)
B′(−4, 12)
B′(−1, −3)
B′(10, −6)

Answer 1

To reflect a point across the line y=3, we find the point that is the same distance from y=3 as the original point, but on the opposite side of the line. In this case, the original point is B(−4,−6), which is 9 units below y=3. The image point will be 9 units above y=3, so it will have a y-coordinate of 3+9=12. The x-coordinate remains the same, so the image point is B
′
(−4,12).