1. Lesson 9.1 – Symmetry and Reflections
Standard G.2.4

2. A Stroll Down Memory Lane…
What kind of shape is this?
A shape is symmetric if it has a line or lines which cuts the shape into two congruent halves

3. Why does symmetry matter?
Balance of shape
Natural Beauty
Real life uses in games such as
Billiards
Ping-Pong
Putt-Putt

4. Examples to Try
How many lines of symmetry do the following shapes have?

5. Lines of Reflection FB <A DC ΔDCF D
Name the image of each figure under reflection in line m. AF
<B ED
ΔDEF
Point D D FB
<A E C DC
ΔDCF D A F B m

6. Coordinate Geometry Write This Slide Down!
We can reflect points in four different ways
Across the x-axis
All y-values switch signs
Across the y-axis
All x-values switch signs
Across the line y = x
x-values and y-values trade spots
Around the origin
All x-values and y-values switch signs
Write This Slide Down!

7. Examples Reflect the line AB in the following ways: Across the x-axis
Across the y-axis
Across the line y = x
Around the origin
A (-3, -2)
B (1, 4)
A (3, 2)
B (-1, -4) y
B (-4, 1)
y = x
A (2, -3)
A (2, -3)
B (-1, 4)
A (3, -2)
B (-4, 1)
A (-3, -2)
B (1, 4)
A (-3, 2)
A (3, -2)
B (-1, 4)
B (-1, -4)
A (3, 2) x
B (1, -4)

8. Homework
Workbook pp