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Similar Polygons
MACC.912.G-SRT.1.1 Verify experimentally the properties of
dilations given by a center and a scale factor:
A dilation takes a line not passing through the center of the dilation
to a parallel line, and leaves a line passing through the center
unchanged.
The dilation of a line segment is longer or shorter in the ratio given
by the scale factor.
MACC.912.G-SRT.1.2 Given two figures, use the definition of
similarity in terms of similarity and transformations to decide if they
are similar; explain using similarity transformations the meaning of
similarity for triangles as the equality of all corresponding pairs of
angles and the proportionality of all corresponding pairs of sides.
Warm Up
1.
5 9
=
x 4
2.
8
4
=
11 x -1
3.
2x +1 x + 2
=
13
9
Warm Up
Complete each congruence statement given that
4.
5.
PC @ _____
ÐHDL@_____
Show work to justify your answer.
6. A cell phone is approximately 4.6 in wide and 8.4 in
long. What is the ratio of the width of the cell phone
to the length?
7. A bonsai tree is 18 in. wide and 2 ft tall. What is
the ratio of the height of the bonsai tree to its width?
Ratios of Sides
(simplest form)
Angle Measures
Conjecture
Group Sharing
Students circulate through gallery walk and
make conjectures.
Students present using document camera or
other technology.
Similar Polygons
Have corresponding angles congruent and the
lengths of corresponding sides proportional
Symbol used for similarity: ~
Similarity statement: written between two figures to
designate corresponding angles and sides
Similar Triangles
Similarity Statement:
JKL~ MNO
K
N
30
20
12
8
L
M
30/12 = 5/2
20/8 = 5/2
15/6 = 5/2
6
15
J
Scale Factor: 5/2
Student Survey
Fist of five
Marzano’s level of understanding
CPS or web survey for instant anonymous
results.
Possible Extensions
Practice Homework sheet/ follow-up.
Given coordinates and a scale factor of a
polygon have students create a similar figure.
Take students outside to complete an activity
where they measure their shadows and height to
find an tree, flagpole, or field goal height.