A full turn around a point equals 360º. If a full turn equals 360º, then the sum of the angles around a point must also be 360º. When you calculate angles around a point, you can use this fact to find ...

The radius of a circle is a line, which starts at the centre of the circle and ends on a point on the circumference. The radius is half the length of the diameter. Looking at the diagram, since OA and ...