Head First 2D Geometry

118 Chapter 3

the rules always apply

In geometry, the rules are the rules

In geometry there’s no “i before e except after c” stuff. The rules

are the rules. Everything in your Geometry Toolbox applies

whether you think, draw, touch, look, play, or test your way to an

answer.

1

3

2

4

Use your BRAIN

Use the REAL

WORLD

Use a PENCIL

and PAPER

Use a COMPUTER

MODEL

Your GEOMETRY TOOLBOX

works with ALL of these methods.

So no matter which of

these methods I use, I’ll

get the same answers?

Yes, you’ll get the same results however

you approach it.

Geometry is nice like that! For practical reasons, we’ll be

using your brain and a pencil and paper for this chapter,

but if you want to make use of the other methods as well

then that’s cool, too.

you are here 4 119

the pythagorean theorem

You’ve already worked out that you can build a ramp from Kwik-klik parts, using lengths 10, 8, and 6.

Which two rules from your Geometry Toolbox can help you quickly find some other lengths that

would also work?

Angles in a four-sided

shape add up to 360º.

If two angles

add up to

90º, they are

complementary

Similar shapes have

the same angles.

Similar shapes have the same

ratios between lengths of sides.

1

2

2

2

4

4

Angles in a

triangle add up

to 180º.

Vertically

opposite angles

are equal.

10

8

6

120 Chapter 3

use similarity

You’ve ...