GEOMETRY: CIRCLES
Apple
piePhone
4
Robert Peppermint
Pattinson Vam-pie-re Pie
Careful: This one bites back.
diameter = 11 inches
circumference:
area:
Celebrate Pi Day
by finding the
circumference
and area of our
homemade pies.
H
appy Pi Day! Pi,
also written as
π, is a number
approximately
equal to 3.14. It
helps us find the circumference
and area of circles. Because
March 14 can be written as 3/14,
it is celebrated as Pi Day. Math
classes and groups worldwide
plan pi-themed events. You may
have noticed on our cover that
this is the March 14 issue of
MATH. So we decided to join in
the fun.
Check out what we’ve baked
up for this year’s pi party. Just
be glad you don’t have to eat
them.
—by Carli Entin
WHAT TO DO
s
iu
d
ra
SCHO L AST I C M ath
➜ Radius (r) is the distance from the center of a circle
to any point on the circle. Diameter (d) is the distance
across a circle through the center. The diameter is twice
the radius: d = 2r
➜ The circumference (C) is the distance around a circle:
C = 2πr = πd
2
➜ Area (A) is the region inside a circle: A = πr
Example: Find the diameter, circumference,
diameter
and area of a circle with a radius of 4 inches.
d = 2 5 4 = 8 inches
C = 3.14 5 8 = 25.12 inches
fe
2
ren
A = 3.14 5 4 = 3.14 5 16 = 50.24 sq. in.
ce
m
6
circumference and area of circles
circu
Read “Circumference and
Area of Circles.” Use that
information to find the
circumference and area of
our special pies. (We’ll ask
you for the radius in one
question.) Use 3.14 for pi.
Justin Bieberry Pie
hair: Rolf Vennenbernd/epa/Corbis; blueberry pie: Alkristeena/Shutterstock; iPhone: courtesy of Apple; apple pie: Gerville Hall/iStockphoto;
Michele: Matthias Clamer/FOX; can of peas: Todd Taulman/Shutterstock; pie shell: Rainbowphoto/iStockphoto
5
1
Justin Bieberry Pie
It takes 1 hour to bake the
pie, and 7 hours to get the hair
just right.
radius = 5 inches
circumference:
3
Apple piePhone
Download the popular
whipped-cream app.
diameter = 14 inches
circumference:
area:
area:
2
Glee Lime
Pie
You’ve heard of
key lime pie. (You
haven’t? Just trust
us; it’s a well-known
pie.) Now try Glee Lime Pie.
Caution: May cause
sudden singing.
radius = 3 inches
circumference:
Pie-rates of the
Carrots, Beans
Arrr! Eat yer veggies, matey, or
you’ll be walkin’ the plank.
radius = 4.5 inches
circumference:
area:
6
Pea-Can Pie
Now with more cans!
area = 314 square inches
radius:
Lea Michele
from Glee
circumference:
Pea-Can
Pie
area:
march 1 4 , 20 1 1
7