Circle Vocabulary

Circle – set of all points _________ from a given point called the _____ of the circle. equidistant C center Symbol: C

CHORD: A segment whose endpoints are on the circle

DIAMETER: Distance across the circle through its center P Also known as the longest chord.

RADIUS: Distance from the center to point on circle P

Radius = ½ diameter or Diameter = 2r Formula Radius = ½ diameter or Diameter = 2r

D = ? 24 32 12 r = ? 16 r = ? 4.5 6 D = ? 12 9

Use P to determine whether each statement is true or false. Q R T S True: thumbs up False: thumbs down

Secant Line: intersects the circle at exactly TWO points

Tangent Line: a LINE that intersects the circle exactly ONE time Forms a 90°angle with one radius Point of Tangency: The point where the tangent intersects the circle

An angle whose vertex is at the center of the circle Central Angles An angle whose vertex is at the center of the circle

Angle APB is a Central Angle 3 Types of Arcs Major Arc A Minor Arc More than 180° Less than 180° ACB P AB To name: use 3 letters C To name: use 2 letters B Angle APB is a Central Angle

Semicircle: An Arc that equals 180° D E To name: use 3 letters P EDF F

THINGS TO REMEMBER A circle has 360 degrees A semicircle has 180 degrees Vertical Angles are CONGRUENT Linear Pairs are SUPPLEMENTARY

Formula for Central Angles measure Arc = measure Central Angle

Find the measures. NP is a diameter. m MN = 100° m MPN = 260° m PMN = 180°

Arc Addition Postulate B m ABC = + m BC m AB

150 230 130 280 m GE = m GEF = m GF = m FHE = Tell me the measure of the following arcs. m GE = 150 O 230 m GEF = m GF = 130 280 m FHE =

Congruent Arcs have the same measure and MUST come from the same circle or of congruent circles. B D 45 45 110 A

Practice Worksheet