GeoGebra Tutorials

1. Geometry Calculator

2. Contents
Transformations -Rotation

3. Transformations
Task -Rotation
In this tutorial, we are going to learn how to rotate a polygon
by a given angle using a slider and enhance our construction
by hiding all Auxiliary Objects in the Algebra View

4. Rotation
Create an arbitrary
triangle ABC in the
first quadrant placing
the vertices on grid
points.
Triangle A,B,C

5. Rotation
Create a new point D
at the origin of the
coordinate system.
Point D

6. Rotation
Rename the point D to
O.
Hint: Select point D
and just type O to
open the Rename
dialog
Point O

7. Rotation
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 ̊(degree)
symbol
Check Angle

8. Rotation
Use the Rotate around
Point tool to rotate
triangle ABC around
point O by angle α.

9. Rotation
Hints: Activate the tool
and select the triangle
before you select the
center of rotation. In the
appearing dialog, enter
α as the angle through
the Virtual Keyboard
and choose counter
clockwise rotation.
Use Virtual Keyboard
to enter α
Enter α as the angle
Choose counter clockwise

10. Rotation
Create segments AO
and A’O

11. Rotation
Create angle AOA’.
Hint: Select the points
in counter clockwise
order.

12. Rotation
Hide the label of angle
AOA’
Uncheck Show Label

13. Rotation
Move the slider and
explore the image of
the triangle

14. 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. 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.

15. Rotation
Select all segments in
the Algebra View.
Hint: Click on the
heading Segment in
order to select all
segments at the same
time
Select all segments

16. Rotation
Open
the Settings for the
segments using
the Style Bar and
check Auxiliary
Object on tab Basic
Check Auxiliary Object

17. Rotation
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’.
Algebra View now contain required points

18. Rotation
You can color and style
the segments. Add the
other segment not
added earlier on.
Note: You can now show
or hide the Auxiliary
Objects by toggling
the Auxiliary Objects
button in Algebra View
Style Bar.

19. Rotation
Animate and observe
what happens.

20. END
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