
202 Chapter 4
your geometry toolbox
Your Geometry Toolbox
You’ve got Chapter 4 under
your belt and now you’ve
added properties of triangles
to your toolbox. For a complete
list of tool tips in the book, head to
www.headfirstlabs.com/geometry.
CHAPTER 4
Area =
1/2 base x height
The height comes from the
altitude of the triangle—it’s
perpendicular to the base.
Perimeter
Add up all the sides of
your shape to find the
perimeter.
Hero’s formula
Area = s (s-a) (s - b) (s - c)
s = a + b + c
2
Find the semiperimeter first,
then use it to find area.
Centroid
The point where all three
medians of the triangle
intersect
Median
A line from the midpoint of a
side to the opposite vertex
Incenter
The center of a circle drawn
inside the triangle, touching
every side
Circumcenter
The center of a circle drawn
outside the triangle, through
every vertex
Orthocenter
The point where all three
altitudes of the triangle
intersect