Do you think the three angles in a triangle have any special relationship to one another?
Do you think that the exterior angle <CBD, has any relationship to any of the angles inside the triangle? Make a conjecture in your notebook answering these questions.
Next, use the angle measurement tool to measure the three angles in the triangle as well as the exterior angle <CBD.
Add all three angles together from the interior of the triangle. What do you notice? Do you think this will always be true for every triangle? (Write your answers in your notebook using complete sentences.)
Next, add up the two interior angles <C and <A. What do they add up to? What other angle is their sum equivalent to? Write your findings in your notebook.
Next, drag a one or more vertices of the triangle around. Add up the three interior angles of the triangle again. Write what you have learned into your notebook.