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Head First 2D Geometry by Dawn Griffiths, Stray

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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.
202 Chapter 4
Area =
1/2 base x height
T
he height comes f
rom the
a
lti
tude of the tr
iangle—i
t’s
p
er
pendicul
ar t
o the base.
Per
imeter
Add up a
ll the sides of
y
our shap
e to find the
p
er
imeter.
Hero’s f
ormul
a
Area = s (s-a) (s - b) (s - c)
s =
a + b + c
2
F
ind the semip
erimeter fir
s
t,
then use i
t t
o find ar
ea.
Centroid
T
he p
oint where a
ll thr
ee
medians of the triangle
intersec
t
Median
A line f
rom the midp
oint of a
side t
o the opposite vertex
Incenter
T
he c
enter of a circle drawn
inside the tr
iangle, t
ouching
ev
ery side
Circumcenter
T
he c
enter of a circle drawn
outside the tr
iangle, through
ev
ery v
ertex
Orthoc
enter
The point wher
e all thr
ee
altitudes of the tr
iangle
inter
sec
t
their own TV s
how in
Head F
ir
s
t Algebra.
triangle properties
TriangleGrid Solution
Stop the press! Your buddies have secretly lined up
a headline act for the festival. Solve the grid puzzle
to be the rst to know who the mystery band are.
Mys
tery band
1
T A
P Y T H A G O R E A N
2
C O M P L E M
E N R Y
3
C A
J U L Y
4
V E R
T I L A N G L E S
5
S I M I L A R
6
F A C T O R T R E E
7
A L T
I T U D E
8
C O N
G R U E N T
9
S U P L E MP
E N T A R Y
10
ET R I P L S
11
H Y P O T E N U S E
Clues
1. You use this theorem to find missing sides of right triangles.
2. Two angles adding up to 90º are known as this.
3. The month before August.
4. When lines cross, they create equal and opposite pairs of these.
5. If shapes have equal angles but are different sizes they are this.
6. To find common factors you can use one of these.
7. The height of a triangle is the length of this.
8. If triangles are similar and the same size then they are this.
9. Two angles adding up to 180º are know as this.
10. 3-4-5 and 5-12-13 are examples of Pythagorean ........
11. The longest side of a right triangle is called this.
Are y
ou a P
ajama Dea
th
f
an? Help the band get
you are here 4 203

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