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Reflections of Graphs (AQA GCSE Maths)
Revision Note
Reflections of Graphs
How do we reflect graphs of functions?
In relation to y = f(x);
- y = -f(x) represents a reflection in the x-axis (up/ down)
- y = f(-x) represents a reflection in the y-axis (left/ right)
How do reflections of graphs work?
It's useful to understand that;
- y = -f(x) reverses the sign all of the function's -coordinates: that's why it gets reflected in the up/down direction.
- Similarly, y = f(-x) reverses the sign of all the of the function's x-coordinates: that's why it gets reflected in the left/right direction.
How do we describe reflections of graphs?
- Some questions give a transformed function in the form y = f(−x) or y = −f(x) and ask you to describe the transformation
- To describe a reflection fully, you must include;
- the transformation: "reflection"
- the direction; in the x-axis or in the y-axis
- Remember that
- if the "−" is inside the bracket, its a reflection in the y-axis
- if the "−" is outside the bracket, its a reflection in the x-axis
Examiner Tip
REMEMBER that;
- y = f(−x); "−" next to x, reflects left/right (reflection in the y-axis)
- y = −f(x); "−" not next to x, reflects up/down (reflection in the x-axis)
Worked example
The graph of is shown on the grid below.
(a) On the grid, draw the graph of .
(b) On the grid, draw the graph of .
(a) Reflect in the y-axis
(b) Reflect in the x-axis
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