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Head First 2D Geometry
book

Head First 2D Geometry

by Stray (Lindsey Fallow), Dawn Griffiths
November 2009
Beginner content levelBeginner
368 pages
8h 55m
English
O'Reilly Media, Inc.
Content preview from Head First 2D Geometry
you are here 4 231
circles
Area of a circle = r
2
Use the circle area formula to work out the area of the pizza in each
deal. Is MegaSlice really a better value?
It’s true—if you crammed enough narrow triangles into a circle,
eventually you’d get a perfect fit. You’d need an infinite number of
triangles, but it turns out the number of triangles cancels neatly, so
wham—you just found the formula for the area of a circle!
If your sectors
are small enough,
eventually it’s a
perfect fit.
r
2
They actually need to be REALLY
small, much smaller than this, but
if we drew them that small they’d
be impossible to see!
If your calculator doesn’t have a
Pi button then you can use 22/7
to get an approximate value for Pi.
With enough (infinite)
triangles there are no
rough edges.
mario’s is the better value
232 Chapter 5
Use the circle area formula to work out the area of the pizza in each
deal. Is MegaSlice really a better value?
Area = r
2
Mario’s 18” pizza: radius = 18 = 9 inches
2
Area =
x 9
2
= x 81 = 254.5 sq inches
MegaSlice 12” pizza: radius = 12 = 6 inches
2
Area = 2 x
x 6
2
= 2 x x 36 = 226.2 sq inches
18”
12” 12”
2 pizzas
Mario’s is MORE!
Q:
Eek—2πr and πr
2
look pretty similar don’t you think? Is
there a way to keep them straight so I don’t mix them up?
A: There are a couple ...
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Publisher Resources

ISBN: 9780596808365Errata Page