posted by Cindy .
The coordinates of the vertices of CDE are C(1, 4), D(3, 6), and E(7, 4). If the triangle is reflected over the line y = 3, what are the coordinates of the image of D?
This one is fairly easy. The x-coordinates do not change, since we are rotating around a horizontal axis.
For the y-coordinates, just figure the distance above or below y=3, and change them to the same distance below or above.
(1,4) is 1 unit above y=3. Make it one unit below: (1,2)
(3,6) -> (3,3-(6-3)) = (3,0)
(7,4) -> (7,3-(4-3)) = (7,2)