circles honors math – grade 4. circle a circle is a plane figure. all the points on a circle are...

Circles

Honors Math – Grade 4

Circle

A circle is a plane figure.All the points on a circle

are the same distance from a given point, called the center.

Point A is the center of the circle

A

A circle is named by its center point.

Circle A

The Parts of Circle B

EC

B

D

F

G

All the line segments in Circle B have special names.

Can you name any points on the circle?

E, C, D, F, G

Radius

A radius is a line segment with endpoints at the center of the circle and on the circle.

is a radius.

Can you name any other radii (plural of radius)?

BC

EC

B

D

F

GBD

BE

Diameter

A diameter is a line segment that passes through the center of the circle and has both endpoints on the circle.

is a diameter.

EC

B

D

F

G

CD

The length of the diameter is always equal to twice the length of the

radius.If BE measures 6 cm, how long is CD?

12 cm

Chord

A chord is a line segment with both endpoints on the circle.

is a chord. Are there any other

chords in Circle B? Line segment CD

EC

B

D

F

G

FG

A diameter is a special chord.

Simple Closed Curve

A simple closed curve is a path that begins and ends at the same point and does not cross itself.

Not simple closed curves

Simple Closed Curves

Practice

1. Name the circle and its center.

2. How many diameters are shown? Name the diameters.

3. Is TR a radius? Explain why or why not?

4. Is VX a radius? Explain why or why not?

5. How many radii are shown? Name the radii.

R SV

X

Q

W

T

P

Practice Answers

1. ____________________________________________

2. ____________________________________________

3. ____________________________________________

4. ____________________________________________

5. ____________________________________________

Practice Answers

1. Circle V. The center is point V.2. There are 3 diameters. PQ, RS, TW3. TS is not a radius because it does not

have an endpoint at the center of the circle and it is a chord.

4. VX is a radius because its endpoints are the center point V and point X on the circle.

5. There are 7 radii. VP, VS, VW, VQ, VX, VR, VT