10-1Circles and Circumference

You identified and used parts of parallelograms.

• Identify and use parts of a circle.

• Solve problems involving the circumference of a circle.

Definition

A circle is the locus of points in a plane equidistant from a given point.

That point is the center of the circle.

center

Circle Parts

A circle is named by its center.

A radius is a segment from the center to any point on the circle.

A diameter is a segment that contains the center of the circle and has endpoints on the circle.

Qּס

Qּס

radius

diameter

Definition

A chord is a line segment that joins two points on a circle.

AB is a chord of ּסD

Where would you find the largest chord in any circle?

A

B

D

p. 697

A. Name the circle and identify a radius.

B. Identify a chord and a diameter of the circle.

A. Name the circle and identify a radius.

A.

B.

C.

D.

B. Which segment is not a chord?

A.

B.

C.

D.

By definition, the distance from the center of a circle to any point on the circle is always the same. All radii of a circle are congruent. A diameter (d) is made is made up of two radii.

1 raduis 1 raduis

p. 698

Answer: QV = 10.5 cm

d = 2r Diameter Formula

21 = 2r d = 21

10.5 = r Simplify.

If RT = 21 cm, what is the length of QV?

RT is a diameter and QV is a radius.

A. 12 cm

B. 13 cm

C. 16 cm

D. 26 cm

If QS = 26 cm, what is the length of RV?

Exterior, Interior, Concentric

interior

exterior

Concentric circles are two coplanar circles with the same center.

p. 698

5

A. 3 in.

B. 5 in.

C. 7 in.

D. 9 in.

10-1 Assignment Day 1

p. 701, 10-21