10-9 reflections (page 456-459)
DESCRIPTION
10-9 Reflections (page 456-459). Indicators G7-Identify the line & rotation symmetries of 2-d figures to solve problems. G8-Perform reflections of 2-d figures using a variety of methods. Reflections…. Figures that match exactly when folded in half have line symmetry . - PowerPoint PPT PresentationTRANSCRIPT
10-9 Reflections (page 456-459)
Indicators G7-Identify the line & rotation symmetries
of 2-d figures to solve problems.G8-Perform reflections of 2-d figures using a variety of methods.
Reflections…
Figures that match exactly when folded in half have line symmetry.
Each fold line is called a line of symmetry. Some figures can be folded in more than one way to show symmetry.
You try…
• Determine whether each figure has line symmetry. If so how many? Where?
• A type of transformation where a figure is flipped over the line of symmetry is a reflection.
• Think of a mirror image. • As with translations, the original
figure and reflected image are congruent.
ReflectionReflection (flip)(flip)
Helpful Hints!Helpful Hints!
•When reflecting over the x-axis, change the When reflecting over the x-axis, change the y-coordinate to their opposites.y-coordinate to their opposites.
•When reflecting over the y-axis, change the When reflecting over the y-axis, change the x-coordinate to their opposites.x-coordinate to their opposites.
Example: Reflect a figure over the x-axis.
Quadrilateral QRST has vertices Q (-1,1),R (0,3), S (3,2), T (4,0).Find the coordinates of QRST after a reflection over the x-axis. Then graph the figure and its reflected image.
Q
RS
TQ’
R’S’
T’
The coordinates for the reflected image are Q (-1,-1), R (0,-3), S (3, -2), T (4,0). Check out the y-coordinates!
Example 2: Reflect a figure over the y-axis.
Triangle XYZ has vertices X (1,2),Y (2,1), Z (1,-2). Find the coordinates of XYZ after a reflection over the y-axis. Then graph the figure and its reflected image.
X
Y
Z
X1
Y1
Z1
The coordinates for the reflected image are X (-1,2), Y (-2,1), Z (-1,-2). Check out the x-coordinates!
Example 3: Reflect a figure over the x-axis.
Triangle XYZ has vertices X (1,2),Y (2,1), Z (1,-2). Find the coordinates of XYZ after a reflection over the x-axis. Then graph the figure and its reflected image.
X
Y
ZX’Y’
Z’
The coordinates for the reflected image are X (1,-2), Y (2,-1), Z (1,2). Check out the y-coordinates!
Homework
• 10-8 pg. 453-454 #6-12 e, 16-26 a10-8 pg. 453-454 #6-12 e, 16-26 a• 10-9 pg. 459 #16-27 a10-9 pg. 459 #16-27 a