Warm UpDecode these words and phrases.1. Mind 2. LU CKY Matter

3. water 4. stand swimming do you

Warm Up Continued…

MR DUCKSMR NOT DUCKS

MR 2 DUCKSCM WANGS

LIB MR DUCKS

Lesson 4.1: Circumference of a

CircleI can:Identify the radius and

diameter of a circle.State the formula for

circumference of a circle.

Find the radius and diameter of a circle, given the circumference.

Vocabulary:RadiusDiameterCircumferen

cePi

Center of a Circle

The point in a circle which all points on the circle are equidistant from.

Radius

The distance from the center of a circle to a point on the circle.

Diameter

The distance across a circle through its center point.

CircumferenceThe distance around the edge of a circle. (Perimeter of a circle)

*the red

indicates

Circumference

Pi

The circumference of any circle, divided by its diameter. We will denote pi by the number 3.14.

* If you take any circle and find the circumference and diameter, no matter what the size circle, you will always get Pi .

FormulasIf we know the radius and we

are trying to find the circumference, we use

If we know the diameter and we are trying to find the circumference, we use dC

rC 2

Example 1:1. We know our formula to find the circumference, given the radius, is2. Now, all we have to do is plug in the values given to us into our equation and solve.

12.2514.3842

2

CCC

rC

4

rC 2

Example 2:1. We know our formula to find the circumference, given the diameter,is2. Now, all we have to do is plug in the values given to us into our equation and solve.

4.311014.3

10

CCC

dC

10

dC

Try these examples:

25

22

2.56

Answers:

25

22

2.56

15769.08

7.8537.68