Head First 2D Geometry

you know how to find area

280 Chapter 7

Hot tub volume is area x depth

Calculating the volume of some 3D shapes can get pretty

gnarly, but for the hot tub range it’s simple. The tubs have

straight sides, so the volume can be found from area × depth.

Length

Same depth all over

Q:

This book is called Head First 2D

Geometry, right? So how come we’re

talking about 3D in this chapter?

A: Volume is definitely a 3D topic, and

we cover it in much more detail in Head

First 3D Geometry, but it’s not too bad to

dip your toes in the water is it? Also, we’re

about to turn this problem back into a 2D

one on the next page.

Q:

You’re going to turn a 3D problem

into a 2D problem? How does that

work?

A: The third dimension in the hot tubs

problem is depth. Once we don’t have to

work with the depth anymore it’s just a 2D

problem we’re left with. Hold that thought

to the bottom of the next page.

Q:

What if the tub was deeper at

one end than the other? Or had curved

sides?

A: The area × depth formula only

applies to 3D shapes with straight sides, all

of the same depth, which are perpendicular

to the base. If the hot tub was deeper

at one end we’d need a different way of

working out its volume.

These “straight-sided” shapes are

known as prisms—more about those

in Head First 3D Geometry.

[Thanks! Marketing xx]

AREA = length x width

Width

you are here 4 281

regular polygons

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