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Head First 2D Geometry by Dawn Griffiths, Stray

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OK, y
ou could kind of nibble the
circumf
er
ence if y
ou w
anted....
compare areas
What property of the pizzas do you need to compare to be able to
work out whether MegaSlices claims are true?
Area
If you put “V
olume” her
e, you’r
e right,
but as all Mar
io’s p
izzas hav
e the same
thickness, ar
ea will also cov
er i
t. Mor
e on
tha
t in C
hapter 7!
We need to find the area of the two pizza deals
MegaSlice offers two 12" pizzas for the same price as one of
Mario’s 18" pizzas.
So, which deal is more AREA of pizza, because that’s the
property you actually get to eat.
W
hich is mor
e?
18"
12"
12"
224 Chapter 5
circles
Well, I’m not sure we even need
to work this one out. Two times
twelve is more than eighteen, so
MegaSlice’s deal is more pizza.
Frank: Not so fast. I’m not sure it’s that simple.
Joe: What’s hard about it? 12 + 12 = 24. 24 is way more
than 18. Game over.
Jim: But that’s not area—that’s diameter!
Joe: Yeah—and?
Jim: Well, I’m not sure that you can just add up diameters
and then compare them instead of comparing area.
Joe: Why not? Anyway, we don’t even know how to find
the area of a circle. Hey—is this making you guys hungry?
Frank: Shut up! This is serious. We need to find a way to
compare the actual pizza area, and not just the diameters.
Jim: Agreed, but where do we start?
Frank: Well, I guess we should just start from what we do
know and go from there.
Which technique from your Geometry Toolbox could help you
work out the pizza areas approximately?
T
r
iangle ar
ea
= 1/2 base x
height
Simil
ar
i
ty and
congruenc
e
Angles in a
quadr
ila
tera
l
add up t
o 360º.
Frank
Jim
Joe
you are here 4 225

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