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Circles

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Circles

Honors Math – Grade 4

A

- 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

Circle A

A circle is named by its center point.

C

E

B

D

G

F

- All the line segments in Circle B have special names.
- Can you name any points on the circle?
- E, C, D, F, G

C

E

B

D

G

F

- A radius is a line segment with endpoints at the centerof the circle and on the circle.
- is a radius.
- Can you name any other radii (plural of radius)?

C

E

B

D

G

F

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

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

12 cm

If BE measures 6 cm, how long is CD?

C

E

B

D

G

F

- 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

A diameter is a special chord.

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

Simple Closed Curves

Not simple closed curves

P

T

V

S

R

X

W

Q

- Name the circle and its center.
- How many diameters are shown? Name the diameters.
- Is TR a radius? Explain why or why not?
- Is VX a radius? Explain why or why not?
- How many radii are shown? Name the radii.

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- Circle V. The center is point V.
- There are 3 diameters. PQ, RS, TW
- TS is not a radius because it does not have an endpoint at the center of the circle and it is a chord.
- VX is a radius because its endpoints are the center point V and point X on the circle.
- There are 7 radii. VP, VS, VW, VQ, VX, VR, VT