Circumference and Area of a Circle

The set of points equidistant from a given point called the center

Circumference - the distance around the circle

Diameter - the distance across the circle, through the center

Radius - The distance from the center to any point on the circle

The diameter is twice as long as the radius.

d = 2r

The radius is half the length of the diameter.

r = d/2

The ratio of a circle's circumference to its diameter.

Used to calculate the circumference and area of a circle.

 $\pi$  =  $\frac{C}{d}$  
 $\pi$   $\times$  d =  $\frac{C}{d}$   $\times$  d
 $\pi$  d = C
C =  $\pi$  d

Formulas:

C =  $\pi$  d

1. Write the formula

2. Substitute the values

3. Multiply

4. Write the unit of measure

A =  $\pi$   $r^2$  

1. Write the formula
2. Substitute the values
3. Simplify
4. Write the unit of measure  $units^2$