Head First 2D Geometry

70 Chapter 2

the phone’s size is important

It’s a problem of scale…

The design Liz picked was originally created in 2007, when

phones were a lot bigger than the one Liz has today. In fact,

the design is twice as big as the space available on the back of

Liz’s phone for etching!

2007 phone

Today’s phone

…but how big a problem is it?

myPod-designs-(c) 2007

This design needs to

be updated to fit on

today’s smaller gadgets.

Q:

How come there weren’t any units on the drawing? If

they’d put units we could have seen whether it fit before we

started etching.

A: You’re right, we could have. In this case, though, the lengths

on the diagram wouldn’t be normal measures like millimeters or

inches, but a special measure used by the etching machine.

Q:

But shouldn’t the drawing still have a scale? Wouldn’t

we be best to add one now?

A:For now we can just adjust the lengths we’ve got to work

with—we can safely assume that whatever units the etcher uses,

they aren’t going to change before we etch again. But in the next

chapter we’re going to look at using scales in a lot more detail.

you are here 4 71

similarity and congruence

Pool Puzzle

Your job is to take steps from the pool

that you think will help you make

the design fit on Liz’s new phone,

and use them to complete your

to-do list. (You don’t need ...