Reflection (In x-axis, y-axis, x = a, y = a and the origin; Invariant Points)
296. Mirror Across the X-Axis · Reflecting a point across the x-axis using construction tools
P′ is the reflection of P across the x-axis — same x-coordinate, opposite y-coordinate.
Reflecting in the x-axis sends (x, y) → (x, −y): the x-coordinate is unchanged and the y-coordinate changes sign. P and its image are equidistant from the x-axis, with PP′ perpendicular to it.