Question

The point (2, –4) is reflected across the line y = –1. What are the coordinates of the image?

A.(–5, –4)
B.(–4, 2)
C.(2, 2)
D.(2, 4)

Answer 1

Hint:
r_{y=k): (x,y)->(x,-(y-k)+k)
or simplified,
r_{y=k): (x,y)->(x,2k-y)

So in this case, k=-1, x=2, y=-4
(2,-4) -> (2, 2(-1)-(-4)
(2,-4) -> (2, -2+4)
(2,-4) -> (2, 2)