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Coordinates, graphs and transformations
Lesson 69 of 75
Challenge

Reflections

Objective. Reflect points and shapes in horizontal and vertical lines.

  1. 1. Learn
  2. 2. Worked example
  3. 3. Practice
  4. 4. Feedback
  5. 5. Continue

Learn: the key idea

A reflection is a transformation that flips a shape over a mirror line, creating an image that is the same size and shape as the original but reversed. Every point on the reflected image is the same perpendicular distance from the mirror line as the corresponding point on the original shape, but on the opposite side. Reflecting in the line x=0 (the y-axis) keeps the y-coordinate the same but reverses the sign of the x-coordinate, so (3,2) becomes (−3,2). Reflecting in the line y=0 (the x-axis) instead reverses the sign of the y-coordinate.

Worked example

Reflect the point (4, −5) in the x-axis and state the coordinates of its image.

4 … 5
Coordinate grid with the line 4 … 5
  1. 1Identify the mirror line: the x-axis, where y=0.
  2. 2Reflecting in the x-axis keeps the x-coordinate the same.
  3. 3Reverse the sign of the y-coordinate: −5 becomes 5.
  4. 4Write the final image coordinates.

Answer: (4, 5)

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Practice

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Common mistake. Pupils sometimes reflect a shape by sliding it across the page rather than flipping it, producing a translated image instead of a mirror image. Always check that the image is the same perpendicular distance from the mirror line but on the opposite side.

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