| Mirror Line | What Happens | Example |
|---|---|---|
| x-axis (y = 0) | y changes sign, x stays same | (3,4) → (3,-4) |
| y-axis (x = 0) | x changes sign, y stays same | (3,4) → (-3,4) |
| y = x | x and y swap | (3,4) → (4,3) |
| y = -x | x and y swap, both change sign | (3,4) → (-4,-3) |
| x = a (vertical) | Reflect horizontally in vertical line | (1,3) in x=3 → (5,3) |
| y = b (horizontal) | Reflect vertically in horizontal line | (2,1) in y=3 → (2,5) |
This key facts covers Common Mirror Lines within Transformations: Reflections for GCSE Mathematics. Revise Transformations: Reflections in Geometry & Measures for GCSE Mathematics with 13 exam-style questions and 5 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 2 of 6 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Transformations: Reflections
A point P has coordinates (3, 5). It is reflected in the x-axis. What are the coordinates of its image P'?
Fully describe the single transformation that maps shape A onto shape B. Shape A has vertices at (1, 1), (3, 1), (3, 4) and shape B has vertices at (−1, 1), (−3, 1), (−3, 4).
Quick recall flashcards
Reflecting in y = -x
Swap coordinates AND change both signs. (x,y) → (-y,-x). Example: (3,4) → (-4,-3)
Reflecting in y = x
Swap x and y coordinates. Example: (3,4) → (4,3)