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

CHORD: a segment whose ________ are on the circle

RADIUS: distance from the _____ to a point on the circle center P

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

What is the relationship between the diameter and the radius of a circle? OR D = ½ D 2 r

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

SECANT sounds like second Secant Line A secant line intersects the circle at exactly TWO points. SECANT sounds like second

TANGENT: a LINE that intersects the circle exactly ONE time

Point of Tangency

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

Two circles can intersect… in two points one point or no points

No points of intersection (different center)

No points of intersection (same center) Concentric Circles Same center but different radii

1 point of intersection (Tangent Circles) Externally Tangent Internally Tangent

2 points of intersection

<APB is a Central Angle Central Angle : An Angle whose vertex is at the center of the circle A Major Arc Minor Arc 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° To name: use 3 letters E D EDF P F

THINGS TO KNOW AND REMEMBER ALWAYS A circle has 360 degrees A semicircle has 180 degrees Vertical Angles are Congruent

measure of an arc = measure of central angle 96 Q m AB = 96° B C 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. D 140 260 m BCA = R 40 100 80 C B

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