http://www.ck12.org Chapter 12. Rigid Transformations
12.1 Exploring Symmetry
Learning Objectives
- Learn about lines of symmetry.
- Discuss line and rotational symmetry.
- Learn about the center of symmetry.
Review Queue
- Define symmetry in your own words.
- Draw a regular hexagon. How many degrees does each angle have?
- Draw all the diagonals in your hexagon. What is the measure of each central angle?
- Plot the pointsA( 1 , 3 ),B( 3 , 1 ),C( 5 , 3 ), andD( 3 , 5 ). What kind of shape is this? Prove it using the distance
formula and/or slope.
Know What?Symmetry exists all over nature. One example is a starfish, like the one below. Draw in the line(s) of
symmetry, center of symmetry and the angle of rotation for this starfish.
Lines of Symmetry
Line of Symmetry:A line that passes through a figure such that it splits the figure into two congruent halves.
Many figures have a line of symmetry, but some do not have any lines of symmetry. Figures can also have more than
one line of symmetry.
Example 1:Find all lines of symmetry for the shapes below.
a)