Congruency, Enlargement and Combined Transformations
Rotation
A transformation that turns a shape about a fixed centre by an angle and direction.
| English | Rotation |
|---|---|
| Bahasa Melayu | Putaran |
| 中文 | 旋转 |
How it is used
Rotate the point P(3, 0) by 90° anticlockwise about the origin. The image is P′(0, 3), because a 90° anticlockwise rotation sends (x, y) to (−y, x).
Where it shows up in SPM
One of the isometric transformations in this Form 5 chapter. Paper 2 asks you to draw a rotated image or to describe a rotation fully with its angle, direction and centre.
It is a common component of combined transformations such as a rotation followed by a translation.
Don't confuse it with
Open the chapter: Congruency, Enlargement and Combined Transformations →
Frequently asked questions
What must I state to describe a rotation fully?
State three things: the angle (for example 90°), the direction (clockwise or anticlockwise), and the centre of rotation as coordinates. A 180° rotation is the one case where direction does not matter, since clockwise and anticlockwise give the same image.
How do I find the centre of rotation?
Join each object point to its image point, then draw the perpendicular bisector of two such lines. Where the bisectors cross is the centre of rotation, because it is equal distance from every point and its image.