
Visualizing Transformations (applet)
Choose a
transformation and apply it to a shape to observe the resulting
image. 
Task
The goal of this task is to explore the effects of applying various transformations to a shape. Eventually you should be able to predict how each transformation will change the shape's image. Consider the red shape in the interactive figure below. Drag it and observe the behavior of its image, shown as a black outline. Choose a different shape, and using the same transformation, observe the behavior of its image. Change the shape of the red square or the red triangle by dragging it by an edge or vertex while pressing the "Control" key. Change the orientation by dragging the shape by a vertex. Describe the position and orientation of the resulting image in relation to the original shape. What is the relationship between the side lengths and angle measures of the original shape and those of the resulting image? Now consider the same tasks using other transformations.
How to Use the Interactive Figure
To observe the behavior under the selected transformation, drag or change the red shape. To select a shape, click on the shape in the icons at the top. To select a transformation, click on the icons on the left. Change the shape of the red square or red triangle by dragging from an edge or vertex while pressing the Control key. Change the orientation of the red square or red triangle by dragging it from a vertex. Resize the circle by dragging it from any point on the circumference.
 Reflection
To change the slope of the reflection line, drag the line. To change the position of the line, drag the point on the line.
 Translation
To change the translation, drag the arrow from any of its endpoints.
 Rotation
To change the angle of rotation, drag the angle symbol from the upper endpoint. To change the center of rotation, drag the blue dot at the vertex.
Discussion
Dynamic geometry software
allows students to visualize a transformation by manipulating a shape and
observing the effect of each manipulation on its image. By focusing on the
positions, side lengths, and angle measures of the original and resulting
figures, middlegrades students can gain new insights into congruence.
Transformations can become an object of study in their own right. Teachers can
ask students to visualize and describe the relationship among lines of
reflection, centers of rotation, and positions of preimages and images. Using
the interactive figure, students might see that the result of a reflection is
the same distance from the line of reflection as the original shape. In a
rotation, students might note that the corresponding vertices in the preimage
and image are the same distance from the center of rotation and all the angles
formed by connecting the center to the corresponding vertices are congruent in
the image and the preimage.
Take Time to Reflect
 What new insights into congruence can students gain as they work on activities like this?
 What relationships between the original shape and its image are important for students to note in a translation?
 What relationships between the original shape and its image are important for students to note in a reflection?
 What relationships between the original shape and its image are important for students to note in a rotation?
Also see:
 6.4 Understanding Congruence, Similarity, and Symmetry Using Transformations and Interactive Figures
 6.4.2 Identifying Unknown Transformations
 6.4.3 Composing Reflections
 6.4.4 Composing Transformations