# Circle Geometry; cyclic quadrilaterals

- Author:
- DavidA

- Topic:
- Angles, Circle, Geometry, Quadrilaterals

**An illustration of the angle properties to be found in a cyclic quadrilateral.**Circle Theorems http://www.geogebratube.org/student/c89/m1462/yryy

**This is a nice theorem to prove algebraically.**As a start to your proof you could mark the centre of the circle and draw in the radii to the vertices of the quadrilateral. A nice alternative is to draw the diagonals and use another popular circle theorem that you can see illustrated here http://www.geogebratube.org/student/m1462