6th Grade Math Textbook, Fundamentals

 &KDSWHU

10-10

A complete rotation is 360.

A half rotation is 180.

A quarter rotation is 90.

Symmetry

Objective To identify line symmetry and lines of symmetry, rotational

symmetry, and point symmetry• To draw figures that have line symmetry,

rotational symmetry, or point symmetry

In the flower shown at the right, the dashed line divides

the flower into mirror-image halves. If you were to fold the

flower along the dashed line, the two halves would match

exactly. If you turn the flower one fifth of a full turn, the

rotated flower would look the same as the original.

Are there other imaginary lines that divide the flower

into mirror-image halves? Are there other turns that

would create a flower that looks just like the original?

The quality that makes the flower above appear

“balanced” is called.

A figure has if a real or imaginary line

divides the figure into mirror-image halves. This line is

called the. When you fold a figure in

half along a line of symmetry, the two sides match each

other exactly.

In the picture of the butterfly at the right, the blue line

is a line of symmetry. If you were to fold the picture on

the line, the halves would match.

The green line is nota line of symmetry. If you were to

fold on the green line, the halves would not match.

The flower shown at the top of the page has five

lines of symmetry.

A figure has if it matches the

original figure after rotating less than a full turnaround

a central point. This point is called the center of rotation.

The center of rotation may be a point on the figure, or it

may be some other point.

The smallest turn that creates a match is an.

To find its measure, count the number of times a figure can be

rotated within a full turn. Then divide 360 by this number.

A multiple of the angle of rotation also creates a match.

angle of rotation

rotational symmetry

line of symmetry

symmetry

line symmetry