Part III of proof that the angles in a triangle add up to 180 degrees. Other ways of proving this triangle property: - Proof video 2 (similar but different method): Proof video 1 using parallel lines and transversal: Chapters: 0:00 intro and video purpose 0:45 setting up the proof structure 2:05 getting angles in the triange - first angle 3:06 getting the second angle 3:52 getting the third angle 5:11 calculating the sum of the angles Subscribe to TinyMaths here: