Answer:
(2, - 5)
Step-by-step explanation:
The line y = -1 is horizontal: parallel to the y-axis.
The point B (2,3) is above the line y = - 1 at a distance equal to the y-coordinate of B (y = 3) less - 1:
Δy = 3 - ( - 1) = 4
When the point B (2,3) is reflected over the line y = -1, the x-coordinate does not change. The image will be 4 units down the line y = -1, thus the y-coordinate will be - 1 - 4 = - 5.
Hence, the coordinates of the vertex B' are x = 2, y = - 5: (2, - 5).