CHAPTER 7
your geometry toolbox
Your Geometry Toolbox
You’ve got Chapter 7 under
your belt and now you’ve
added regular polygons to
your toolbox. For a complete list
of tool tips in the book, head over to
www.headfirstlabs.com/geometry.
Ar
ea =
1/2
x P
erimeter
x Ap
othem
P
erimeter =
Number of sides
x Side length
Equil
ateral
tr
iangle ar
ea =
3 t
2
4
Circumradius:
radius of the circumcircle
Ap
othem:
radius of the incircle
Internal angle
=
(n x 180º) - 360º
n
(n is number of sides)
The apothem joins the center to the
middle of a side, bisecting it.
The circumradius joins the center to
a vertex.
The apothem meets the side at a
right angle.
The circumradius bisects the
internal angle.
318 Chapter 7
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