GeoGebra Classroom

Exploring Reflections

A reflection is a transformation that uses a line like a mirror to reflect or "flip" a figure. The mirror line is called the "line of reflection." The following activities will help you explore various types of reflections. Like the last exploration, observe how this type of transformation affects the points, segments and angle measures of the figure when creating the image.

Reflection over the y-axis (x = 0)

What are the effects of a reflection over the y-axis on the points, segments and angle measurements?

Reflection over the x-axis (y = 0)

What are the effects of a reflection over the x-axis on the points, segments and angle measurements?

Reflection over a vertical line

What are the effects of a reflection over any vertical line on the points, segments and angle measurements?

Reflection over a horizontal line

What are the effects of a reflection over any horizontal line on the points, segments and angle measurements?

Define Relationships within Reflections

Return to the above GeoGebra sketches. Add lines connecting the original point to its image. Notice the relationship between these lines and the line of reflection.

Summarize the relationships you observed between these new lines and the line of reflection.

Can you do it on your own?

Create a line of reflection using the line tool. Then use the "reflect about a line" tool to create the image.

Reflection over the line y = x

What are the effects of a reflection over the line y = x on the points, segments and angle measurements?

Use the input bar to insert your guess for the line of reflection into the sketch. Then, use the GeoGebra tools to check the accuracy of your line.

What is the equation of the line of reflection used to create the image above?

Reflection Rules

So far you have explored three different scenarios. You should have noticed the following patterns or rules: If a figure is reflected in the y-axis, then all of the points will move according to the rule . If a figure is reflected in the x-axis, then all of the points will move according to the rule . If a figure is reflected in the line y = x , the all of the points will move according to the rule . What do you think is the rule when figures are reflected in the line y=-x?

Challenge 1

Explore what happens when we perform a composition of two reflections. Return to one of the sketches above. Add a second line of reflection. Use the "reflect about a line" tool to reflect the image again. Record the summary of your observations below.

Observations of the effects of a composition of two reflections.