Reflection flips a point across an axis or line. Reflecting (x, y) across the x-axis gives (x, -y). Reflecting across the y-axis gives (-x, y).
Rotation turns a point around the origin. Rotating (x, y) by 90° counterclockwise gives (-y, x). By 180° gives (-x, -y). By 270° gives (y, -x).
These transformations show up in problems involving symmetry, mirroring, or turning shapes.