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Describing a Reflection

(KS2, Year 6)

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. line_of_reflection

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. describe reflection example

describe reflection example

Step-by-Step:

1

Find a point on the shape and the corresponding point on its reflection. describe_reflection_step_1

describe_reflection_step_1

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

2

Join the points with a line. describe_reflection_step_2

describe_reflection_step_2

3

Mark the half way point of this line. describe_reflection_step_3

describe_reflection_step_3

4

Find another point on the shape and the corresponding point on its reflection. describe_reflection_step_4

describe_reflection_step_4

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

5

Join the points with a line. describe_reflection_step_5

describe_reflection_step_5

6

Mark the half way point of this line. describe_reflection_step_6

describe_reflection_step_6

7

Join the half way points with a line. describe_reflection_step_7

describe_reflection_step_7

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. describe_reflection_step_8

describe_reflection_step_8

Answer:

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

describe reflection answer

describe reflection answer

Lesson Slides

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

What Is a Reflection?

A reflection flips a shape so that it becomes a mirror image of itself. A reflection is a type of transformation.

How to Find the Equation of a Line

It is useful to say what the equation of the line of reflection is. The equation of a line can be given in slope-intercept form:

y = mx + c

m is the slope (the steepness) of the line.
c is the y-intercept of the line: where the line crosses the y-axis.

Let us look at the example in this lesson. line_of_reflection_equation_example

line_of_reflection_equation_example

The line goes up by 1 unit for every 1 unit it goes across. The line has a slope of 1.
The line crosses the y-axis at 2. It has a y-intercept of 2.

The equation of the line is:

y = 1x + 2 ∴

y = x + 2

This page was written by Stephen Clarke.

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Worksheet

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