Radius – The distance from the center of the circle to the endpoint.

Diameter – The distance from one endpoint, through the center, to the other endpoint.

Circumference – The distance around the outside of the circle…like perimeter of a circle.

The symbol π (pi)= 3.14. We are going to use π = 3 (Which

is an estimate for π, since there are about 3 diameters in Circumference. )

So whenever you see the symbol π replace it with 3.

What is π?

To find the circumference of a circle, you must use the formulas located on your TAKS Measurement Chart…

If you know the radius, use this circumference formula….. 12 m

C = 2 π r

If you know the diameter, use this circumference formula….. 24 m

C = π d

Step 1 Setup the Problem…LABEL ALL PARTS!

R= 12 m(radius)

D= 24 m(diameter)

12 m

Use C = 2 ∙ π ∙ r, since the radius is given in this problem.

C = 2 ∙ π ∙ ror

C = π ∙ d

Step 2 Choose the Formula…Write it down!

Step 3 Solve the Problem

C = 2 ∙ π ∙ r

C = 2 ∙ 3 ∙ 12

C = 6 ∙ 12

C = 72 m

8 m

Example 2: Try on your own

Diameter = 2 x radius

Diameter = 2 x 8Diameter = 16m

What is the Diameter and Circumference?

C = 2 ∙ π ∙ rC = 2 ∙ 3 ∙ 8

C = 6 ∙ 8C = 48 m

radius

20 ft

Example 3: Try on your own

Radius = Diameter / 2

Radius = 20 / 2Radius = 10 ft

What is the Radius and Circumference?

C = π ∙ dC = 3 ∙ 20C = 60 ft

diameter

Solve the Problem

C = π ∙ d

48 = 3 ∙ d

48 ÷ 3 = d

16 cm = d

Circumference = 48cm, What is the diameter?

Diameter=?