[b]A illustration of the properties of the angles drawn from the ends of a chord in a circle.[/b][br][br]Circle Theorems [url]http://www.geogebratube.org/student/c89/m1462/yryy[/url]

Two important results are the equality of the [b]angles at the circumference[/b] and their connection to the [b]angle at the centre[/b].[br][br]A special case that you are often expected to know is the result when the angle at the centre is 180.[br]When AB becomes a diameter and you have a [b]semi-circle[/b].[br][b]What is significant about the angle at the circumference in this case?[/b]