Reflect a point across the x-axis
The idea
Locate the original point and note its horizontal and vertical coordinates.
Step by step
- Locate the original point and note its horizontal and vertical coordinates.
- Keep the horizontal coordinate and move the same vertical distance to the other side of the x-axis.
- Use (x, y) → (x, −y), then check that the two points are equally far from the axis.
Example
Reflect the point (2, 3) across the x-axis. What are the image coordinates?
Answer
(2, -3)
The horizontal coordinate stays 2. The vertical coordinate changes from 3 to -3, so the image is (2, -3).
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Draw a triangle on grid paper and reflect each vertex across the x-axis. Compare corresponding distances.
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