This document contains notes from a geometry class. It begins with instructions for bell work and then discusses similarity of figures. It defines similar polygons as having proportional corresponding sides and congruent corresponding angles. It states the ratio of perimeters of similar polygons equals the ratio of corresponding sides. The document then discusses methods to prove triangles similar, including AAA, AA, SSS, and SAS. It assigns homework problems from the textbook and worksheet to be due the next class.

1. Geom8­2and8­3.notebook January 19, 2012
Good morning. Please be in your seat quietly
working on the bell work when the bell rings.
Thank you!
BELL WORK:
If eb ­ fc = gb + hc, find the ratio of b to c.
Let's recap on the means­extremes ratio theorem.
nt = rb nt = rb
1

2. Geom8­2and8­3.notebook January 19, 2012
8.2 Similarity
Similar figures have the same shape, but are not always the same size.
They are proportional.
2

3. Geom8­2and8­3.notebook January 19, 2012
In order to produce similar figures that are smaller or larger than
the originals, we reduce or dilate.
This is my friend, Mike.
I want to make a poster of this
gorgeous photo that is 1/3 as big as
this picture.
How tall will my poster be?
Here in geometry class, we will talk about similar polygons.
Definition: In similar polygons,
The ratios of the measures of the corresponding sides are
proportional.
Corresponding angles are congruent.
S T
Y X
D W
3

4. Geom8­2and8­3.notebook January 19, 2012
Remember the homework problem that asked about the ratio of the
perimeters of two squares?
Theorem: The ratio of the perimeters of two similar polygons
equals the ratio of any pair of corresponding sides.
Take a look on p.334. We are going to discuss the sample problems.
4

5. Geom8­2and8­3.notebook January 19, 2012
8.3 ­ Methods of Proving Triangles Similar
What would we need to know about a pair of triangles in order
to prove they are similar?
AAA
AA
SSS~
If there exists a correspondence between the vertices of two
triangles such that the ratios of the measures of the corresponding
sides are proportional, then the triangles are similar.
SAS~
If there exists a correspondence between the vertices of two
triangles such that the ratios of the measures of two pairs of
corresponding sides are equal and the included angles are
congruent, then the triangles are similar.
5

6. Geom8­2and8­3.notebook January 19, 2012
Triangle Congruence Theorems Triangle Similarity Theorems
Take a look at p.340. We are going to talk about the sample problems.
Homework: p.336 #1­7,9,10 and worksheet
due Monday
6