Head First 2D Geometry

214 Chapter 5

relationship between circumference and diameter

The pepperoni perimeter is 3 (and a bit)

times diameter

There’s a pattern: no matter what size the pizza, the pepperoni

perimeter is a little more than three times the diameter.

A circle’s circumference is diameter x Pi

In geometry terms, a circle’s perimeter is called the circumference,

and no matter how big or small that circle is, you can find the

circumference by multiplying the diameter by the same number.

Roughly it’s just barely over three, and we call this number Pi. Pi is

usually written using this symbol:

Pi

25 pieces of pepperoni

32 pieces of pepperoni

50 pieces of pepperoni

25 = 3.123

32 = 3.2

10

50 = 3.125

16

8

π

The circumference of a

circle is given by:

Circumference =

π

D

or

Circumference = 2

π

r

These are equal

because D = 2r.

8"

10"

16"

you are here 4 215

circles

Why do you think “math people” find Pi, or π, more useful

than 3.1415926535897932384626433832795…?

“Pi” is actually a letter from

the Greek alphabet.

It’s used to stand in for the number

that you always get when you divide a

circle’s circumference by its diameter.

You can probably find a Pi

button on your calculator. It

might give you 3.14159, or it

might give you something with

even more decimal places.

Ha ha…very funny. Not.

The chapter is about pizza

and ...