Mathematics for IGCSE & O level - Transformations (Section 6 - No. 39)
If you reflect a point across the x-axis, what happens to its coordinates?
(x, y) becomes (-x, y)
(x, y) becomes (x, -y)
(x, y) becomes (-x, -y)
(x, y) remains unchanged.
Explicación
Reflection across the x-axis changes the y-coordinate to its negative.