Visualizing the Angle Sum in a Triangle

Task

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

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 ̊.

9.		Create angle ζ using the points A’C’B’.
10.		Create angle η using the points C'₁B'₁A'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.