# sum of opposite angles of cyclic quadrilateral

- Author:
- Mathguru

- Topic:
- Angles, Quadrilaterals

We can clearly see the blue graph, it is that of a circle which passes through the point B and has its center at point A. Points C, D, E and F are four points present on the circumference of the circle. A cyclic quadrilateral is drawn by joining these four point C, D, E, and F. Angles CDE, DEF, EFC and FCD are denoted by α, β , y, δ respectively. We can freely move these six points A, B, C, D, E and F. Move these points and observe how the size and positions of the circle and cyclic quadrilateral get changed.

Questions to think about
1. Calculate α + У , what do we observe?
2. Calculate β + δ, what do we observe?