1. DH2004

2. What is a circle? A circle is a set of points equidistant from a fixed point, called the centre.

3. DH2004 Circumference The length round a circle. It is a special name for the perimeter of a circle. c

4. DH2004 Arc One of the two parts between two points on a circumference Arc

5. DH2004 Radius The distance from the centre of a circle to its circumference. The plural of the term is radii. r

6. DH2004 Diameter The distance across a circle through its centre. The diameter, d, of a circle is twice its radius, r, so d=2r d

7. DH2004 Chord A straight line which joins two points on the circumference of a circle Chord

8. DH2004 Segment The region of a circle enclosed by a chord and an arc. Chord Arc Segment

9. DH2004 Tangent A straight line that touches a circle at one point only on the circumference. Tangent

10. DH2004 Sector A portion of a circle enclosed by 2 radii and one of the arcs between them. Sector

11. DH2004 Semicircle One half of a circle. It can be either of the parts cut off by the diameter. Semicircle

12. DH2004 Test