CIRCLES AND CIRCUMFERENC E Circles A circle is

CIRCLES AND CIRCUMFERENC E

Circles A circle is a closed plane figure made up of points which have the same distance from a point called its

center O A circle is named by its center. The circle on the side is called

PARTS OF A CIRCLE Name the circles. A X

RADIUS B O A A radius is a segment from the center to any point on the

OA and OB are radii. (plural for radius) B O A

C Name all the radii. O Y X J D

CHORD E O F A chord is a segment joining two points of a circle.

E O F EF is a chord of circle O.

K H O X J Name all the chords. Y G

DIAMETER E O F A diameter is a chord that passes through the center of the circle.

H O X Name all diameters. L Y G J

Name the radii and the diameter. E O F Compare the length of a radius with the length of the diameter. What can you

Supply the missing term. 1. r= 2. 5 cm, d =___ 2. r= 4 m, d =____

Supply the missing term. 4. d= 9 cm, r =____ 5. d= 37. 5 m, r =____ 6. d=36. 4 dm, r =____

E O C F A An arc is any part of a circle. B FBAE, BAE , EC are arcs of circle O.

E A A O C F semicircle is an arc B that is one half of a circle. Arc

E A O B C F FBAE is a semicircl e.

What parts of the circle is each given? A M 1. 2. 3. T 4. 5. H 6. AH TH MT A MHT HT

CIRCUMFERENCE (C) The distance around a A circle is called circumferen ce. B O

CIRCUMFERENCE (C) Long time ago, mathematicians found out that the ratio of the circumference and the diameter is constant with the value of approximately 3. 14159 or 3. 14 A B O

CIRCUMFERENCE (C) The ratio of the circumference and diameter (the quotient of C and A d)is equal to pi ( ). B O

Formula to be used when the diameter is given:

Formula to be used when the diameter is missing:

Formula to be used when the radius is given:

Formula to be used when the radius is missing:

Find the circumference 1. r = 5 cm 2. d= 1. 7 cm 3. r = 4 m

Find the circumference 4. d= 22 cm 5. r = 61 mm 6. d = 10. 5 m

Find the circumference 7. r = 0. 2 m 8. r = 1. 23 dm 9. d = 0. 08 km

Find the diameter 10. C = 15. 07 units

Examples 1. A circular garden has a radius of 4. 5 m. What is its circumference?

Examples 2. The circular swimming pool has a diameter of 1. 5 metres. If Jackie walks around it, how many metres

Examples 3. Mr. Cada wants to fence his circular bamboo field with wire. How much wire does he need to use if the field

Examples 4. Find the radius of a circular lagoon whose circumference is