GeoGebra Classroom

# Two Parallel Reflections

In this activity, you will investigate reflections over parallel lines. The sketch is located below the 2 investigations.

## Investigation 1

To begin, move the green line to x=0 and the red line to x = 5. Use the green triangle to show the reflection of the original triangle over the green line. Then reflect the green triangle over the red line. Use the red triangle to show this reflection. Click on Answer to check your reflections. Click on the Remove Green Triangle button. Describe how the original triangle could be placed on top of the red triangle without doing two reflections.

## Investigation 2

Click on the Answer and Remove Green Triangle buttons to reset the investigation. Move the vertices of the original triangle to (-4,-1), (-2,4), and (1,1). Next, move the green line to x=-1 and the red line to x = 3. Use the green triangle to show the reflection of the original triangle over the green line. Then reflect the green triangle over the red line. Use the red triangle to show this reflection. Click on Answer to check your reflections. Click on the Remove Green Triangle button. Describe how the original triangle could be placed on top of the red triangle without doing two reflections.

## Question 1

Click on the Red line and move it to x=-1. What happened?

## Question 2

Click on the Red line and continue to move it to different locations. As you move the Red line, you are "sliding" the triangle to different locations. This action is called a translation. As you translate (slide) the triangle to a new location, what doesn't change about the triangle, when compared to the original triangle? What does change?

## Definition

Use your geometry textbook to locate the definition of translation. Write the definition.