1. Rigid Motion in a Plane Translations and Reflections Glide Reflections
Section 7.4 & 7.5
Rigid Motion in a Plane
Translations and Reflections
Glide Reflections

2. Bell Work J’( I,2), K’(4,1) L’(4,-3), M’(1,-3) D’( 4,1), E’(0,2)
F’(2,5)
P’( -1,-3), Q’(-3,-5)
R’(-4,-2), S’(-2,0)

3. Outcomes You will be able to use vector notation to show translations.
You will be able to identify what is a translation, a reflection, or a rotation.
Identify and do a glide reflection or composition.

4. Translations
A translation is a transformation which maps each point of a figure the same distance and in the same direction.
The resulting figure after a transformation is called the image of the original figure, the preimage.
Theorem A translation is an Isometry.

5. Translations

6. Theorem 7.5

7. Theorem 7.5 ΔA’’B’’C’’ k and m AA’’, CC’’ 2.8 in.
Yes, this is the definition of a reflection.

8. Example
Sketch a triangle with vertices A (-1, -3), B (1, -1), C (-1, 0).
Then sketch the image of the triangle after the translation (x, y) ⤍ (x-3, y+4)
Original Image
A (-1,-3) A’( , )
B (1, -1) B’( , )
C (-1, 0) C’( , )

9. Translations EXAMPLE 1:
ΔABC is translated 1 unit right and 4 units up. Draw the image ΔA’B’C’.   
What are the coordinates of:
A (1, -3)  A’ _________
B (3, 0)  B’ _________
C (4, -2)  C’_________
ΔABC  ΔA’B’C’
This translation can be written as (x, y)  (x , y ).

10. Translations J (0, 2)  J’ _________ K (3, 4)  K’ _________
EXAMPLE 2:
 ΔJKL has coordinates J (0,2), K (3,4), and L (5,1).
a) Draw ΔJKL.
b) Draw the image ΔJ’K’L’ after a
translation of 4 units to the
left and 5 units up. Label the triangle.
What are the coordinates of:
J (0, 2)  J’ _________
K (3, 4)  K’ _________
L (5, 1)  L’__________   
Rule: (x, y)  ( , )
Are the figures congruent or similar?
Explain how you know.

11. Translation Example 3: Write a general rule which
describes the translation shown below.
ΔLMN is the preimage.
(x, y)  ( , )

12. Translations EXAMPLE 4:
a) Graph points T(0,3), U(2, 4) and V(5, -1) and connect the points to make a triangle.
b) Translate ΔTUV using the rule
(x, y)  (x - 3, y - 1).
c) In words, describe what the rule says.
 d) Draw the image ΔT’U’V’.
e) Identify the coordinates of ΔT’U’V’. T’ U’ V’
f) Using the image of ΔT’U’V’ perform an
additional translation using the rule (x, y)  (x + 3, y - 3).
State the new coordinates of ΔT”U”V”.
Is this new image congruent or similar to the preimage?

13. Vectors
Vector: is a quantity that has both direction and magnitude, and is represented by an arrow drawn between two points.
Symbol PQ
Component form: ⟨3, 4⟩
Arrow Notation: (x, y) ⟶ (x+3, y+4)

14. ⇀
A) AS = ⟨ 4,-4 ⟩ ⇀
B) MN = ⟨ 0, 4 ⟩ ⇀ ⇀

15. Section 7.5 Glide Reflections and Compositions

16. Glide Reflections
When a translation and a reflection are done one after the other it is known as a glide reflection.
A glide reflection is a transformation in which every point P is mapped onto a point P’’ by the following steps:
A translation maps P onto P’.
A reflection in a line k parallel to the direction of the translation maps P’ onto P’’.
**As long as the line of reflection is parallel to the direction of the translation, it does not matter whether you glide first and then reflect, or reflect first and then glide!**

17. Glide Reflection
Use the information to sketch the image if ΔABC after a glide reflection,
A (-1, -3), B(-4, -1), and C (-6,-4)
Translation: (x,y) ⤍ (x + 10, y)
Reflection: in the x-axis
A’’ ( , ) , B’’ ( , ), C’’ ( , )
If we reversed the order of the transformations (reflection then translation), will ΔA’’B’’C’’ have the same coordinates found in the example?
Yes, because the line of reflection is parallel to the direction of the translation!

18. Compositions
When two or more transformations are combined to produce a single transformation, the result is called a composition.
Theorem 7.6 Composition Theorem:
The composition of two, or more, isometries is an Isometry.

19. Compositions
Sketch the image of PQ after a composition of the given rotation and reflection:
P (2, -2), Q (3, -4)
Rotation: 90 degrees CCW about the origin
Reflection: in the y-axis
Repeat the exercise, but switch the order of the composition; reflection then rotation.
What do you notice?

20. Compositions
Sketch the image of PQ after a composition of the given reflection and reflection:
P (2, -2), Q (3, -4)
Reflection: in the y-axis
Rotation: 90 degrees CCW about the origin

21. Compositions

22. Look over the IP and ask questions