Head First 2D Geometry

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...