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Head First 2D Geometry by Dawn Griffiths, Stray

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CHAPTER 2
your geometry toolbox
Your Geometry Toolbox
You’ve got Chapter 2
under your belt and now
you’ve added Similarity and
Congruence to your toolbox. For a
complete list of tool tips in the book,
visit www.headfirstlabs.com/geometry.
Simil
ar s
hap
es hav
e
equa
l angles.
Simil
ar s
hapes have
the same ra
tios
bet
ween side lengths.
Y
ou can spot simil
ar triangles
from t
wo equa
l angles.
Ac
tuall
y they hav
e thr
ee
angles tha
t ar
e equal, but
as soon as y
ou sp
ot two you
know
tha
t the
third
is
gonna
match, t
oo.
Congruent s
hap
es ar
e
simil
ar and the same size.
Congruent s
hap
es have
angles tha
t ar
e equal, jus
t
like similar s
hapes, but
they’re a
lso the same sca
le.
All squar
es and
circles are simil
ar.
100 Chapter 2
similarity and congruence
There’s some major
construction projects up ahead.
And there’s been a collision
between letters and numbers!
Letters and numbers colliding?
Oh, no! It must be ALGEBRA!
But DON’T TURN BACK!
Instead, check out our FREE (and pain free) downloadable bonus
chapter on algebra and geometry here:
http://www.headfirstlabs.com/geometry
…and find out how YOU can harness the power of algebra to solve
215 geometry problems in one go.
you are here 4 101
this is a new chapter 1
What do you think of my
new dress? It’s on sale.
algebra for geometry
bonus
Finding patterns
You’re probably thinking “Wait! This book is about geometry,
what’s this algebra business?”
Well, there’s a lot of patterns in geometry,
and it turns out that once you spot those patterns, algebra can help you find quick
solutions to gnarly problems. We’ll start by speaking the same language with geometric
notation, and then figure out how to spot geometric patterns and use algebra’s X-factor
to find a simple formula for a complex pattern.
I should probably not
mention how dizzy I feel
right now...

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