Parts of a Circle & Circumference

Textbook page 516IAN page 120

Circumference

Diameter

The circumference of a circle is the distance around the outside of a circle

The diameter of the circle is the distance from one side to the other passing through the centre of the circle

What is circumference?

What is diameter?

Radius

Chord

A chord is a line touching the circumference of the circle at two points

The radius is the line connecting the centre of the circle and the circumference

What is a chord?

What is a radius?

Example 1:Name the circle, diameter, and three radii.

C

A BO

The circle is circle O

AB is the diameter

OA, OB, and OC are radii

Example 2:Find each missing value to the nearest hundredth. Use 3.14 for pi.

(A)

d = 8 ft; C = ?C = πdC ≈ 3.14 . 8C ≈ 25.14 ft

8 ft

Example 2:Find each missing value to the nearest hundredth. Use 3.14 for pi.

(B)

r = 3 cm; C = ?C = 2πrC ≈ 2 . 3.14 . 3C ≈ 18.84 cm

3 cm

Example 2:Find each missing value to the nearest hundredth. Use 3.14 for pi.

(C) C = 37.68 in; d = ? C = πd

37.68 ≈ 3.14 . d37.68 ≈ 3.14 d 3.14 3.1412.00 in ≈ d