Geometry · Transformations
Pre-Image and Image
HSG-CO.A.2
Definition
The pre-image is the original figure, the image is its position after a transformation.
Examples
- The pre-image is labeled ABC; the image after transformation is labeled A'B'C', with primes.
- If the pre-image is a triangle at (0,0), (2,0), (0,3), the image after a translation shifts every point the same way.
Key rule
The image is always labeled with prime marks to distinguish it from the pre-image.
Memory hook
Original is the pre-image; after the move, it's the image — with primes.