Circle Vocabulary Parts of a circle: 1.Radius – a segment inside a circle that starts at the center and ends at a point on the circle.(named with two letters) 2. Diameter – a segment inside a circle that starts at a point on the circle, goes thru the center, and ends at another point on the circle.(named with two letters) 3.Chord – a segment inside a circle that starts and ends at a point on the circle.(named with two letters) 4.Tangent – a line outside the circle that intersects the circle in exactly one place. (named with two letters) 5.Secant – a line that passes thru a circle that intersects the circle twice. (named with two letters) 6. Minor arc – a piece of the edge of the circle that is less than ½ of the circle(less than 180 degrees.)(named with two letters) 7. Major arc – a piece of the edge of the circle that is more than ½ of the circle(more than 180 degrees)(named with three letters) 8. Semicircle – a piece of the edge of the circle that is exactly ½ of the circle(exactly 180 degrees)(named with three letters) 9. Central angle – An angle formed by two radii whose measure is exactly the same as its minor arc. (named with three letters) 10. Inscribed angle – An angle formed by two chords or a chord and a diameter whose measure is ½ of its minor arc. (named with three letters)

Measure Relationships in a Circle Radii and Diameters: 1.If given a radius, multiply by 2 to get diameter. 2. If given diameter, divide by 2 to get radius. (All radii in the same circle are =) Semicircles and Diameters 1.If there is a diameter drawn in a circle, then 2 semicircles are created. 2.The measure of any semicircle is 180. Supplementary and Vertical Angles: 1.Two angles that are next to each other and combine to make a straight line are supplementary. 2.Supplementary angles add to = Vertical angles are angles across from each other on intersecting segments or lines. 4. Vertical angles are = to each other. Central Angles and their Minor Arcs: 1.The measure of a central angle is = to the measure of its minor arc.

Finding Missing Segments Angles and Arc Measures Part 1: A E C B D G H Given that BD = 48, find: 1.CD 2.EG 3.CE Given that CE = 17, find 1.GE 2.CA 3.CD 4.BD

Finding Missing Segments Angles and Arc Measures Part 2: D A B F C H G 1.Name the diameters in the picture. 2.Name the 4 semicircles in the picture 3.How many degrees in each semicircle? 4.Name 2 minor arcs in the picture 5.Name 2 major arcs in the picture 6.Name 2 vertical angles in the picture