# Visualizing the Angle Sum in a Triangle

- Author:
- Edward Knote, Judith , GeoGebra Team German

## Task

Create an interactive figure that allows your students to explore the angle sum in a triangle.

## Instructions

1. | Create a triangle ABC with counter clockwise orientation. | |

2. | Create the angles α, β and γ of triangle ABC. | |

3. | Create a slider for angle δ with Interval 0 ̊ to 180 ̊ and Increment 10 ̊. | |

4. | Create a slider for angle ε with Interval 0 ̊ to 180 ̊ and Increment 10 ̊. | |

5. | Create midpoint D of segment AC and midpoint E of segment AB. | |

6. | Rotate the triangle around point D by angle δ (setting clockwise). | |

7. | Rotate the triangle around point E by angle ε (setting counter clockwise). | |

8. | Move both sliders δ and ε to show 180 ̊. |

## Try it yourself...

## Instructions (continued)

9. | Create angle ζ using the points A’C’B’. | |

10. | Create angle η using the points C'._{1}B'_{1}A'_{1} | |

11. | Enhance your construction using the Style Bar.
Hint: Congruent angles should have the same color. | |

12. | Create dynamic text displaying the interior angles and their values (e.g. enter `α = ` and select α from the list of objects on tab of the Advanced section). | |

13. | Calculate the angle sum by entering `sum = α + β + γ` in the Algebra Input. | |

14. | Insert the angle sum as a dynamic text: `α + β + γ =` and select sum from the list of objects on tab . | |

15. | Match colors of corresponding angles and text using the Style Bar. | |

16. | Fix all texts that are not supposed to be moved by using the Style Bar. |