Reflection (In x-axis, y-axis, x = a, y = a and the origin; Invariant Points)
298. Mirror Through the Origin · Flip both signs, keep the distance
O is always the midpoint of PP', and P' is always (-x, -y) relative to O.
Reflecting in the origin sends (x, y) → (−x, −y) — both signs change. The origin O is the midpoint of the segment joining each point to its image.