Unit 8: Symmetry and Surface Area
Lesson 1
Symmetry – An object or image has symmetry if it is ____________ and can fit onto itself either by
____________ or _____________.
Line of Symmetry - is a line that ____________ a figure into ______ reflected parts where the sides are
identical ___________ images of each other. Figures may have one or more lines of symmetry. Lines of
symmetry can be vertical, horizontal, or oblique (a slanted line).
Vertical
Horizontal
Oblique
Part I – Examples Finding Lines of Symmetry
For each image find the line(s) of symmetry. State the number of lines of symmetry and describe each
one as vertical, horizontal, and/or oblique.
By using a ________________ you can see there is one
_____________ line of symmetry.
You can find ____ lines of symmetry: one
____________ and one _____________.
There are ___ lines of symmetry: one _____________,
one _____________ and two _____________
Part II: Practice
For each of the following shapes:
a) Determine the number of lines of symmetry
b) State the type of line
c) Draw the lines of symmetry (if possible)
Shape
Number of
Lines
Type of Lines
Draw the Lines
.
Using Transformations
Transformations are ways to move geometric figures.
Three types of transformations are:
i)
ii)
iii)
Translation – a slide along a straight line. The slides can be horizontal, vertical, or oblique
Reflection – a mirror image in a line of reflection. A point and its reflection are the same
distance from the line of reflection.
Rotation – spinning the image around its center.
Example of a Translation:
The original triangle on the left has been moved 3 units horizontally to the right.
y
0
x
Describe the translation of the triangle on the left to the new triangle on the right.
y
0
x
The triangle of the right has been translated _____________________________and
_______________________________. This is an oblique slide.
Example of a Reflection
The line of reflection is a line equal distance between the two images. The horizontal line at y = 1.
Both image A and image B are 1 unit from the line of reflection.
y
A
Line of Reflection, y = 1
0
x
B
Practice Drawing a Reflection:
a) Redraw the figure using the y-axis as the line of reflection.
b) Redraw the figure using the x-axis as the line of reflection.
Figure A
Figure B
y
y
0
0
x
Homework Assignment: p. 12 # 4-9, 13, 15, 19, 23
x