Edexcel IGCSE Maths 复习笔记 5.2.1 Transformations - Rotation
What are transformations in maths?
- There are 4 transformations in GCSE Maths – rotation, reflection, translation and enlargement
- All 4 change a shape in some way, useful in things like computer graphics.
- There is some language and notation often used in this topic – the original shape is called the object and the transformed shape is called the image
- Vertices on the object are labelled A, B, C, etc.And on the image they will be A’, B’, C’ etc.If there is a second transformation then they will become A”, B”, C” etc.
Rotation – what do I need to know?
- You need to be able to perform a rotation (on a coordinate grid) as well as spotting and describing a rotation when presented with one
- Rotation has 3 features:
1. Angle of rotation – how far we are going to rotate the shape by
2. Direction – clockwise or anti-clockwise
In the special case of 180° you will not need a direction
3. Centre of rotation – this is the point about which our rotation happens
It does NOT have to be a point that is on the shape nor in the middle of the shape; it can be anywhere
Use tracing paper – it should be available although you will probably have to ask one of the invigilators for it. If you don’t want to do that during the exam, ask at the start – okay so a question may not turn up but if it does at least you’ve got it.Most angles are “nice” – 90°, 180°, etc. Draw an arrow facing “up” on your tracing paper. Then as you rotate it, it’ll be really easy to see when you’ve turned 90° (arrow will be facing left or right), 180° (arrow facing down) and so on.