| A | B |
|---|
| circumference | distance around the circle |
| diameter | distance across a circle through the center |
| radius | distance from the center to the edge |
| radii | plural of radius |
| arc | a part of the circumference |
| sector | a part of the circle which is bordered by 2 radii and an arc |
| concentric circles | 2 or more circles with the same center |
| inscribed polygon | polygon inside a circle, vertices of the polygon are on the circumference of the circle |
| chord | segment passes through the interior of a circle-its endpoints are on the circumference |
| semicircle | half a circle |
| central angle | angle whose vertex is the center of the circle |
| inscribed angle | an angle inside a circle-angle opens to the interior of the circle, vertex is on the circumference |
| 360 | number of degrees in a circle |
| 180 | number of degrees in a semicircle |
| polygon | straight sided closed shape |
