warm up: 1.a _______________ is the set of all points equidistant from a given point called the...

Warm up:1. A _______________ is the set of all points equidistant from

a given point called the _______________.

2. A _______________ is a segment that contains the center of a circle and has both endpoints on the circle.

3. A _______________ is a segment that has one endpoint at the center and the other endpoint on the circle.

4. _______________ have congruent radii.

5. A _______________ is an angle whose vertex is the center of the circle.

Congruent Circles Diameter Circle CenterRadiusCentral Angle

10.6 - Circles and ArcsI can find the measures of central angles and arcs. To find the circumference and arc length.

You can find the length of part of a circle’s circumference by relating it to an

angle in the circle.

• An arc is a part of a circle. One type of arc, a semicircle, is half of a circle. A minor arc is smaller than a semicircle. A

major arc is larger than a semicircle.

• You name a minor arc by its endpoints and a major arc or a semicircle by its endpoints and another point on the arc.

Problem: Naming Arcs

• What are the minor arcs of circle O?

• What are the semicircles of circle O?

• What are the major arcs of circle O that contain point A?


• What are the minor arcs of circle A?

• What are the semicircles of circle A?

• What are the major arcs of circle A that contain point Q?


• What are the minor arcs of circle C?

• What are the semicircles of circle C?

• What are the major arcs of circle C that contain point B?

Arc MeasureArc Measure

• The measure of a minor arc is equal to the measure of its corresponding central angle.

• The measures of a major arc is the measure of the related minor arc subtracted from 360. • The measure of a semicircle is 180.

Adjacent arcs are arcs of the same circle that have exactly one point in common. You can add the

measures of adjacent arcs just as you can add the measures of adjacent angles.

Arc Addition PostulateThe measure of the arc formed by two adjacent arcs is the

sum of the measures of the two arcs.

Problem: Finding the Measures of Arcs

• What is the measure of each arc in circle O?


• What is the measure of each arc in circle C?


• What is the measure of each arc in circle O?

The circumference of a circle is the distance around the circle. The number pi ∏ is the ratio of the circumference of a circle to its

diameter.

Circumference of a Circle

The circumference of a circle is ∏ times the diameter.

C = ∏d

Problem: Finding a Distance

• A 2-ft-wide circular track for a camera dolly is set up for a movie scene. The two rails of the track form concentric circles. The radius of the inner circle is 8 ft. How much farther does a wheel on the outer circle rail travel than a wheel on the inner rail of the track in one turn?


• A car has a circular turning radius of 16.1 ft. The distance between the two front tires is 4.7 ft. How much farther does a tire on the outside of the turn travel than a tire on the inside?


• A merry-go-round has seats that are 7 ft. from the center of the ride and 10 ft. from the center. How much farther does a child seated on the outside loop travel than a child seated on the inside loop in one complete revolution?

The measure of an arc is in degrees, while the arc length is a fraction of the circumference.

Arc LengthThe length of an arc of a circle is the product of the ratio

and the circumference of the circle.

Problem: Finding Arc Length

• What is the length of each arc shown in red? Leave your answer in terms of ∏.


• What is the length of a semicircle with a radius 1.3m? Leave your answer in terms of ∏.


• What is the length of each arc?

After: Lesson Check

• Use circle P at the right to answer each question. For Exercises 5 and 6, leave your answers in terms of ∏.

1. What is the name of a minor arc?2. What is the name of a major arc?3. What is the name of a semicircle?4. What is mAB?5. What is the circumference of circle P?6. What is the length of BD?

Homework:Page: 654, #9 – 17 all, 25, 27, 28, 31, 33, 34