Circumference and area of circles

Pick up your calculator for today’s notes

Radius

CenterDiameter

Circumference

dd = 2= 2r r oror r = r = d d ÷ 2÷ 2

The parts of a circle

Pi () is an irrational number that is often approximated by the rational numbers 3.14 and .22

7

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

The area of a circle is the number of square units needed to cover the circle.

A. Circle with a radius of 4 m C = 2r= 2(4)= 8m

B. Circle with a diameter of 3.4 ft C = d= (3.4)

= 3.4ft

Find the circumference of each circle, both in terms of and to the nearest hundredth. Use 3.14 for .

= 25.12 m= 8 * 3.14

= 10.676 ft

= 3.4 * 3.14

= 10.68 ft

4m

3.4 ft

A = (42)

= 50.24 in2

A. Circle with a radius of 4 in.

Find the area of each circle, both in terms of and to the nearest hundredth. Use 3.14 for .

B. Circle with a diameter of 3.4 m

(1.72)

= 2.89 m2

d2 = 1.7

A = r2

= 16in2

= 16 * 3.14

A = r2

= 9.07 m2

= 9.0746 m2

= 2.89 * 3.14

4in

3.4 m

C = d

= 176 ft

= (56) 22 7

22 7

What is the circumference of a circle with a diameter of

56 feet? Use for .

56 1

22 7

= (56)

8 1

22 1

1

8

=

=

56 ft

Remember, we are multiplying so we are allowed to cancel before getting our answer