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

WRITE THIS DOWN AND TELL ME WHY ALL CIRCLES ARE SIMILAR

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

Secant Radius Diameter Chord Tangent Name the term that best describes the notation. Secant Radius Diameter Chord Tangent

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

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

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

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

Formula measure Arc = measure Central Angle

Find the measures. EB is a diameter. C Q 96 E m AB = 96° m ACB = 264° m AE = 84°

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

240 260 m DAB = m BCA = Tell me the measure of the following arcs. AC is a diameter. D A m DAB = 140 240 R 40 100 80 260 m BCA = C B

Congruent Arcs have the same measure and MUST come from the same circle or of congruent circles. B D 45 45 110 A Arc length is proportional to “r”

Textbook p. 396 #11 p. 404 #11 – 16, 25 – 30, 38