Tangents (and incircle)
What about this?
What is the perimeter of the triangle for the largest grey circle? What is the area of the red part of the triangle that is outside the grey circle?
yanelli bisecting segments and angles
Theorem 5 and 6
Sum of Exterior Angles
Stage 4 transformations (translation, reflection,rotation)
Sri Yantra 1.61
Sum of Exterior Angles Triangle
A theorem on regular n-gons (n is even)