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Head First 2D Geometry
book

Head First 2D Geometry

by Stray (Lindsey Fallow), Dawn Griffiths
November 2009
Beginner content levelBeginner
368 pages
8h 55m
English
O'Reilly Media, Inc.
Content preview from Head First 2D Geometry
58 Chapter 2
similar triangles have the same angles
Similar triangles don’t just look the same
Similarity is a key piece of geometry jargon. If two shapes are similar, then
they don’t just look alike, one is an exact scaled version of the other. This
means that they have the same (equal) angles.
But don’t take our word for it…check that it all adds up:
Line part way up
the triangle
Tick marks to show that
our line is parallel
These triangles are similar. In
geometry terms, we don’t just
mean they kinda look the same.
Similar triangles
don’t have to be
the same way up.
86°
53°
41°
86°
53°
41°
86
o
41
o
53
o
41
o
53
o
86
o
41°
53°
86°
Take a big triangle, and draw
a line part way up the triangle,
parallel with the base.
1
This creates a mini triangle
which shares the angle at the
peak of the big triangle.
2
you are here 4 59
similarity and congruence
Using what you know about parallel lines and the F pattern, find the two
mystery angles to complete the mini triangle you’ve created.
If the line is drawn parallel to one of the other sides, do you still end up with the
same angles in your mini triangle?
Remember the F, N, Z patterns
from chapter 1? No? Check out
page 40.
?
?
86
o
41
o
53
o
?
?
41
o
86
o
53
o
41
o
86
o
53
o
?
?
60 Chapter ...
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Publisher Resources

ISBN: 9780596808365Errata Page