| A | B |
|---|
| Concentric Circles | Circles that have the same center - like a bulls eye target or circle ripples in the water. |
| Congruent Circles | Circles that are the same size, i.e. circles that have congruent radii. |
| Chord | A segment that connects two points ON the circle - the diameter is a very unique chord because it specifically passes through the center of the circle, whereas most chords do not. |
| Area | equals pi times radius squared |
| Circumference | equals diameter times pi (or 2 times pi times radius) |
| Distance from Center to Chord | A segment that connects the center of the circle to the midpoint of the chord. This segment is also perpendicular to the chord. When radii are drawn to the endpoints of the chord, an isosceles triangle with altitude/median is shown. |
| Congruent Chords | Are the same distance from the center of the cirlcle. If chords are conguent, then arcs are congruent too. |
| Central Angle | An angle whose vertex is located AT the center of the circle. Angle measure = Arc measure. When on the SAME circle OR on CONGRUENT circles, if the central angles are congruent, then the arcs are congruent, and if the arcs are congruent, then the chords are congruent. |
| Minor Arc | An arc whose measure is less than 180 degrees, named with two letters. |
| Major Arc | An angle whose measure if more than 180 degrees, named with three letters. |
| Semicircle | An arc whose measure is exactly 180 degrees, named with two or three letters. |
| Congruent Arcs | Have the same measure AND are located on either the SAME circle OR on CONGRUENT circles. |
| Secant | A line that passes THROUGH the circle thus containing a chord of the circle, i.e. intersects the circle at exactly two points. |
| Tangent | A line that intersects a circle at ONLY ONE point, i.e. a line that just grazes the circle. |
| Radius Drawn to the Point of Tangency | is perpendicular to the tangent. |
| Congruent Tangents | drawn to the same circle from the same external point. |
| Internally Tangent Circles | Circles that intersect at ONLY ONE point, with one circle located inside of the other. |
| Internally Tangent Line | A line that is simultaneously tangent to two different circles, having one circle on each side of the line. |
| Externally Tangent Circles | Circles that intersect at ONLY ONE point, with neither circle passing through the other. |
| Externally Tangent Line | A line that is simultaneously tangent to two different circles, having both circles on the same side of the line. |
