Hi all I was wondering if someone could help with the following:- I have a regular octagon. Find angle CBA, ACB, BAC. Lines BA and AC are equal in length. I have done the following:- Found all the internal angles and all the external angles. I know that I have an isosceles triangle because BA & AC are equal so the base angles are equal. My guys felling is that I need to divide 135 by 2 to get 67.5, so my base angles ate 67.5, 67.5 and my third angle is 45. But I cannot explain why I dividing 153 by 2 gives the correct answer can anyone explain?