Circles

Parts of a Circle

centerF

Use the center to name a circle.

Circle F

F

Parts of a Circle

Segments & Lines

chord

diameter

radius

tangent secant

Formulas

• Radius/diameter

• Circumference

radius = ½diameter r = ½ d

diameter = 2(radius) d = 2r

C = 2∏r or C = ∏d

Types of AnglesCentral angle

- Vertex is on the center.

Inscribed angle- Vertex is on the circle.

Types of Arcs

P

M

O

major arc

minor arc

semicircle N

MO

MNO

MON

Measure of Arcs & Anglesminor arc = its central angle

major arc = 360 - its central angle

68°

68°

360 – 68 = 292

292°

Measure of Arcs & Anglesminor arc = its central angle

major arc = 360 - its central angle

semicircle = 180

180°

Measure of Arcs & Anglesminor arc = its central angle

major arc = 360 - its central angle

semicircle = 180

inscribed angle = ½minor arc

68°34°

Arc and Chord Relationships

If chords are congruent,

then arcs are congruent.

A

B

C

D

CDAB then AB CD

Arc and Chord Relationships

If a diameter is perpendicular

to a chord, then it bisects the

chord.

A

B

K

KBAKABGH

G H

Arc and Chord Relationships

If a diameter is perpendicular

to a chord, then it bisects the

arc.

A

B

K

ABGH

G H

AH BH

Arc and Chord Relationships

Two chords are if and only if

they are the same distance

from the center.

A

B

C

D

P O

R

PRPOCDAB