Visualizing the Angle Sum in a Triangle


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


1.Toolbar ImageCreate a triangle ABC with counter clockwise orientation.
2.Toolbar ImageCreate the angles α, β and γ of triangle ABC.
3.Toolbar ImageCreate a slider for angle δ with Interval 0 ̊ to 180 ̊ and Increment 10 ̊.
4.Toolbar ImageCreate a slider for angle ε with Interval 0 ̊ to 180 ̊ and Increment 10 ̊.
5.Toolbar ImageCreate midpoint D of segment AC and midpoint E of segment AB.
6.Toolbar ImageRotate the triangle around point D by angle δ (setting clockwise).
7.Toolbar ImageRotate the triangle around point E by angle ε (setting counter clockwise).
8.Toolbar ImageMove both sliders δ and ε to show 180 ̊.

Try it yourself...

Instructions (continued)

9.Toolbar ImageCreate angle ζ using the points A’C’B’.
10.Toolbar ImageCreate 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.Toolbar ImageCreate 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.Toolbar ImageCalculate the angle sum by entering sum = α + β + γ in the Algebra Input.
14.Toolbar ImageInsert 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.