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5.9 Study Guide

Circles

Learning Goals

5.9 The student will identify and describe the diameter, radius, chord, and circumference of a circle.

Vocabulary

Circle - A set of points on a flat surface (plane) with every point an equal distance from a given point called the center.

Chord - A line segment that extends between any two unique points of a circle

Circumference – The distance around the edge of a circle

Radius - A line segment that extends between the center and the circumference of the circle

Diameter - A special chord that goes through the center of a circle.

Examples and Explanations

Circles are named for the center point. The circumference of a circle is the perimeter

of the circle. It is equal to about three times

the diameter. (c ≈3d) lt is equal to about six times the radius. (c≈6r)

A chord can connect any two points a circle.

Chords are line segments. This chord is [pic].

The diameter is a special chord. It passes

through the center of the circle. The diameter

of this circle AC.

The radius line segment that extends between

the center and the circumference of the circle

The radii in this circle are DS , DG and DO The diameter is equal to twice the radius. (d=2r)

The radius is half the diameter. (r=[pic])

Sample Questions

1. Point B is the center of the circle shown.

Which of the following best describes

A Chord

B Radius

C Diameter

D Circumference

2. Which statement about circles is true?

A The radius is twice the diameter

B The circumference is three times the radius

C The diameter is twice the radius

D The circumference is twice the diameter

3. Which line segment represents the diameter of the circle below? Record your answer in the box.

4. What point is used to name the circle below?

A point A

B point B

C point F

D point D

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a

c

b

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