Lesson 9-4: Reflection and
Rotational Symmetry
We will identify when a plane figure has
rotational symmetry
And
I will identify and distinguish between
reflectional and rotational symmetry.
October 18, 2016
A "Line of Symmetry" is the imaginary line
where you could fold the image and have both
halves match exactly. A line of symmetry can
be an actual line in the figure, or it may be
imaginary. A figure may have any number of
lines of symmetry, including an infinite number.
15. For each figure shown below, draw all of
the lines of symmetry.
Figures such as squares have rotational
symmetry, meaning that a rotation of less than
360° can map the shape onto itself. The
smallest such angle is the angle of rotational
symmetry .
Identify whether these figures have rotational
symmetry, reflectional symmetry, or both. Also
identify the angles of rotational symmetry and lines
of reflectional symmetry.
a. isosceles triangle
b. equilateral triangle
Reflectional
1 line of symmetry
Both
3 lines of symmetry
Rot. symmetry of 120˚
Identify whether these figures have rotational
symmetry, reflectional symmetry, or both. Also
identify the angles of rotational symmetry and lines
of reflectional symmetry.
c. rhombus
d. regular hexagon
Both
2 lines of symmetry
Rot. symmetry of 180˚
Both
6 lines of symmetry
Rot. symmetry of 60˚