Have you noticed that certain shapes or objects match when folded
in half? Take for example a magazine or a book, each half matches
the other. It would
look very funny if a book’s front and back didn’t match
when the book is closed!
The reason the front and back of a book matches when it is closed
is because it has line symmetry. When an object is folded along
its line of
symmetry
the two halves
match. A line of symmetry divides
an object into two mirror images. One side is a reflection of the
other.
Take a look at the picture
below.
The dotted line shows the line of symmetry. A line of symmetry
can be a vertical line, a horizontal line, or a diagonal line.
How can you find the lines of symmetry for an object?
Fold the
figure in half. If the two sides match, then the fold is a line
of symmetry.
An object can have more than one line of
symmetry. For example you can fold a rectangle in half horizontally,
vertically,
or diagonally, and each half matches the other. A rectangle has
four lines of symmetry.
If you turned a rectangle upside down, would it look the same?
Yes! This is called turn symmetry.
If an object looks the same when it is turned, it has turn
symmetry.
These objects have turn symmetry.
How can you find if an object has turn symmetry? Turn
the figure. If it looks the same as it did before,
it has turn symmetry.
An object has line symmetry
if you can fold the object, and one half looks exactly like
the other. An object has turn symmetry if you can turn it
part way around and it still looks the same. An object can
have either line or turn symmetry, or both line and turn
symmetry, or no symmetry at all.
EXERCISES
Use
pencil and paper to solve the following:
Use the figures below to answer the following
questions.
1.
Which figure(s) have one line of symmetry?
2.
Which figure(s) have more than one lines of symmetry?
3.
Which figure(s) have turn symmetry?
4.
Is it possible to have a figure with turn symmetry
but not line symmetry?
5.
Find 3 figures in real life that have lines of symmetry.
REVIEW
Use pencil
and paper to solve the following:
Write each fraction as a decimal to the nearest
hundredth. Use a calculator if necessary.
