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

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

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

5.  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?

6. 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

7.  Step 1 Setup the Problem…LABEL ALL PARTS!  R= 12 m (radius)  D= 24 m (diameter) 12 m

8.  Use C = 2 ∙ π ∙ r, since the radius is given in this problem. C = 2 ∙ π ∙ r or C = π ∙ d  Step 2 Choose the Formula…Write it down!

9.  Step 3 Solve the Problem C = 2 ∙ π ∙ r C = 2 ∙ 3 ∙ 12 C = 6 ∙ 12 C = 72 m

10. 8 m Example 2: Try on your own Diameter = 2 x radius Diameter = 2 x 8 Diameter = 16m What is the Diameter and Circumference? C = 2 ∙ π ∙ r C = 2 ∙ 3 ∙ 8 C = 6 ∙ 8 C = 48 m radius

11. 20 ft Example 3: Try on your own Radius = Diameter / 2 Radius = 20 / 2 Radius = 10 ft What is the Radius and Circumference? C = π ∙ d C = 3 ∙ 20 C = 60 ft diameter

12.  Solve the Problem C = π ∙ d 48 = 3 ∙ d 48 ÷ 3 = d 16 cm = d Circumference = 48cm, What is the diameter? Diameter=?