Transformations · Year 9
In Year 9 you learn: describing transformations fully.
A transformation moves a shape. Reflections, rotations and translations keep the size and shape the same (the image is congruent); an enlargement changes the size by a scale factor but keeps the shape (the image is similar).
Key facts
- Rotation: give the angle, direction and centre. 180° about the origin: (x, y) → (−x, −y).
- Enlargement: give the scale factor and centre; every length is multiplied by the scale factor.
- Areas scale by the scale factor squared.
Worked examples
Example 1
Describe the single transformation that maps triangle A onto triangle B.
Answer: A reflection in the y-axis (the line x = 0)
Example 2
Rotate P(4, 1) through 90° anticlockwise about the origin. Where does it land?
Answer: (−1, 4)
Example 3
Enlarge P(3, 2) by scale factor 2 with centre (1, 1).
Answer: (5, 3)