Double-click on the movie to PLAY.

Click once to PAUSE.

RELOAD the page or double-click to return to the START of the movie.

Method C3

Here chord DC is joined to the centre by means of the two lines DO and CO.

Study the completed rotation carefully. Can you explain why angle DOB must be 2 times 56˚?

The next page consists of a JAVA worksheet that allows you to explore the situation more fully by moving the positions of C, D and B.