Reflection flips a shape over a line — the mirror line (or axis). The image is the same size and shape, just back-to-front, like your face in a mirror.
Flip the shape
Flip: in the y-axis
Each point (x, y) maps to (−x, y). Distances and angles stay the same — only the handedness flips.
original image
What reflection keeps and changes
- Kept: lengths, angles, area — the image is *congruent* to the original.
- Changed: orientation flips (clockwise becomes anticlockwise) — a left hand reflects to a right hand.
- Every point and its image are the same distance from the mirror line, on opposite sides; the mirror line is the perpendicular bisector of the join.
- Points on the mirror line don't move — they're fixed.
Your turn
Reflect the point (3, 2) in the y-axis. Where does it land?
Watch out
A reflection is not the same as a rotation of 180°. Both 'turn the shape around', but a reflection reverses orientation (mirror image) while a half-turn doesn't. Check a lopsided shape like the 'F' above to tell them apart.