# Visualizing the Angle Sum in a Triangle

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 ̊.

## Instructions (continued)

 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.