How to Describe a Reflection

Describing a Reflection

A shape can be reflected. Every point on the shape is reflected in a line of reflection.

To describe a reflection, we need to say where the line of reflection is.

The Line of Reflection

The line of reflection is a mirror line. It is the line a shape is reflected in.

The image below shows a shape reflected in a line of reflection.

How to Describe a Reflection

Describing a reflection is easy.

Question

Describe how the light blue shape below has been reflected to make the dark blue shape.

Step-by-Step:

1

Find a point on the shape and the corresponding point on its reflection.

We will choose point A on the shape. Point A' is the corresponding point on the reflection.

2

Join the points with a line.

3

Mark the half way point of this line.

4

Find another point on the shape and the corresponding point on its reflection.

We will choose point B on the shape. Point B' is the corresponding point on the reflection.

5

Join the points with a line.

6

Mark the half way point of this line.

7

Join the half way points with a line.

We have found the line of reflection.

We can find the equation of the line.

8

Find the equation of the line.

The equation of the line is y = x + 2.

Answer:

The shape has been reflected in the line y = x + 2:

Slider

The slider below shows another real example of how to describe a reflection.

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See Also

What is geometry? What are transformations? What is a linear equation in slope-intercept form? What is slope? What is the y-intercept?