Skip to Main Content
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
you are here 4 81
similarity and congruence
Similar shapes that are the same size are congruent
Shapes that are similar have equal angles and are proportional, but if
they’re actually the exact same size, then we say that they’re congruent.
The big arrows and
the small arrows are
SIMILAR but not
CONGRUENT.
They’re not congruent
because even though they are
similar, one is smaller than
the other.
These three arrows
are congruent.
These three
arrows are
congruent.
How can spotting congruence save you even more time and work
than similarity?
Congruent
Two shapes are congruent
if they’re similar and also
the same size.
Two shapes are incongruent
if they are not the same
size.
82 Chapter 2
make your problem smaller
But calculating the
corner angles of squares and
equilateral triangles is the easy
part! How’s congruence going
to help with all those angles
between the arrows? Huh?
For starters, congruence means you
only have to do one third of the work.
Those overlap angles are much trickier, but you’ll only
have to find each one once—then you can just copy it
to each of the angles congruent with it.
Original
Problem
Smaller
Problem
Similarity &
Congruence
Look how much of
the problem just
vanished!
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Make: Geometry

Make: Geometry

Joan Horvath, Rich Cameron
Classical Geometry: Euclidean, Transformational, Inversive, and Projective

Classical Geometry: Euclidean, Transformational, Inversive, and Projective

I. E. Leonard, J. E. Lewis, A. C. F. Liu, G. W. Tokarsky

Publisher Resources

ISBN: 9780596808365Errata Page