Drag the vertices of the triangle. Notice the changes in the angle measures.
1) Are there any restrictions on the angle measures?
2) What do you notice about the sum of the angle measures?
Click the box that says "Show Parallel Line." Again drag the vertices of the triangle and notice the changes in the angle measures.
3) What do you notice about the measures of the orange angles? How could you prove that this is always true?
4) What do you notice about the measures of the green angles? How could you prove that this is always true?
5) What is the relationship between the three angles that share a vertex at B?