AGENDA 1. Pass back test 2. Notes on Circles 3. Notes on Central Angles 4. Practice / Homework Worksheet

C

Parts of a Circle

Circle

– set of all points _________ from a given point called the _____ of the circle.

Symbol:

C

CHORD:

A segment whose endpoints are on the circle

Radius

P

RADIUS:

Distance from the center to point on circle

Diameter

P DIAMETER:

Distance across the circle through its center

Also known as the longest chord.

D = ?

r = ? r = ? D = ?

Use



P to determine whether each statement is true or false .

Q

1 .

RT

is a diameter.

False

R

2 .

PS

is a radius.

True



P

3 .

QT

is a chord.

True

T S

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 a radius

Point of Tangency: The point where the tangent intersects the circle

Name the term that best describes the notation.

Central Angle : An Angle whose vertex is at the center of the circle A Major Arc Minor Arc More than 180° Less than 180° P ACB To name: use 3 letters C B AB To name: use 2 letters 

APB is a Central Angle

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

THINGS TO KNOW AND REMEMBER ALWAYS

A circle has 360 degrees A semicircle has 180 degrees Vertical Angles are Equal

measure of an arc = measure of central angle

A E Q 96

 m AB = 96° m ACB = 264° m AE = 84°

C B

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

Tell me the measure of the following arcs.

m DAB =

240

 D A m BCA =

260

 140  40  80  100  C B

Congruent Arcs have the same measure and MUST come from the same circle or of congruent circles.

C B D 45 45 110 A Arc length is proportional to “r”

Classwork • Practice Worksheet