Rotating Polygons
Task
Learn how to rotate a polygon by a given angle using a slider and enhance your construction by hiding all Auxiliary Objects in the 
Algebra View.
Algebra View.Instructions
| 1. |  | Create an arbitrary triangle ABC in the second quadrant placing the vertices on grid points. |
| 2. |  | Create a new point D at the origin of the coordinate system. |
| 3. |  | Rename the point D to O. Hint: Select point D and just type “O” to open the Rename dialog. |
| 4. |  | Create a slider for angle α. Hint: In the Slider dialog window, check Angle and set the Increment to 90 ̊. Make sure you don’t delete the ̊ symbol. |
| 5. |  | Use the tool Rotate around Point in order to rotate triangle ABC around point O by angle α. |
| Hints: Activate the tool and select the triangle before you select the center of rotation. In the appearing dialog, enter α as the angle and choose counter clockwise rotation. | ||
| 6. |  | Create segments AO and A’O |
| 7. |  | Create angle AOA’. Hint: Select the points in counter clockwise order. |
| 8. | 
| Hide the lable of angle AOA’. |
| 9. |  | Move the slider and explore the image of the triangle. |
Try it yourself...
Enhance your construction
You will now learn how to ‘tidy up’ the Algebra View by defining some objects as Auxiliary objects and hiding their algebraic representation from view. Thus, your students will be able to explore the coordinates of the initial points and their images in the Algebra View without being distracted by the algebraic representations of the other objects used in this construction.
Note: You can now show or hide the Auxiliary Objects by toggling the 
Auxiliary Objects button in 
Algebra View Style Bar.
Algebra View by defining some objects as Auxiliary objects and hiding their algebraic representation from view. Thus, your students will be able to explore the coordinates of the initial points and their images in the Algebra View without being distracted by the algebraic representations of the other objects used in this construction.
| 1. |  | Show the Algebra View using the  View menu. |
| 2. |  | Select all segments in the Algebra View.
Hint: Click on the heading Segment in order to select all segments at the same time. |
| 3. |  | Open the  Properties dialog for the segments using the  Style Bar and check Auxiliary Object on tab Basic. |
| 4. | | Repeat the last two steps for the triangles, angles and point O at the origin.
Hint: The Algebra View now only contains points A, B, and C as well as their images A’, B’, and C’. |
Auxiliary Objects button in Algebra View Style Bar.