Mathematics
Grade 10
15 min
Compositions of congruence transformations: graph the image (Tutorial Only)
Compositions of congruence transformations: graph the image (Tutorial Only)
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1
Introduction & Learning Objectives
Learning Objectives
Define a composition of transformations and identify its components.
Graph the image of a figure after a sequence of two or more congruence transformations.
Apply the coordinate rules for reflections, translations, and rotations in a specific sequence.
Use prime notation (P -> P' -> P'') to track a point through multiple transformations.
Describe a single transformation that is equivalent to a given composition, such as two reflections over parallel lines.
Verify that a composition of congruence transformations results in an image that is congruent to the preimage.
Ever wonder how animators make a character walk and turn in a video game? 🤖 They're using a sequence of moves, just like we will today!
This tutorial will teach you...
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Key Concepts & Vocabulary
TermDefinitionExample
Composition of TransformationsThe process of applying two or more transformations in a specific order to a figure. The image of the first transformation becomes the preimage for the second transformation.A translation of 2 units right, followed by a reflection across the x-axis.
Congruence Transformation (Isometry)A transformation in which the resulting image is congruent to the original preimage. The size, shape, and angle measures are preserved. Translations, reflections, and rotations are all congruence transformations.Reflecting a triangle across the y-axis produces a new triangle with the exact same side lengths and angle measures.
Preimage and ImageThe preimage is the original figure before any transformations are applied. The image is the new figure that resul...
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Core Formulas
Composition Notation
(T_2 \circ T_1)(P) = T_2(T_1(P))
This notation represents a composition of transformations. The transformation on the right (T_1) is applied first to the point P. Then, the transformation on the left (T_2) is applied to the result of the first transformation.
Translation Rule
(x, y) \rightarrow (x + a, y + b)
This rule translates a point 'a' units horizontally and 'b' units vertically. If 'a' is positive, the shift is right; if negative, left. If 'b' is positive, the shift is up; if negative, down.
Reflection Rules
Across x-axis: (x, y) \rightarrow (x, -y) \quad | \quad Across y-axis: (x, y) \rightarrow (-x, y) \quad | \quad Across y = x: (x, y) \rightarrow (y, x)
These are the coordinate rules for reflecti...
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Challenging
A figure is reflected across the vertical line x = 2 and then reflected across the vertical line x = 5. Which single transformation is equivalent to this composition?
A.reflection across the line x = 3.5
B.translation 3 units to the right
C.translation 6 units to the right
D.180° rotation
Challenging
Consider the composition of a 90° CCW rotation about the origin followed by a 180° rotation about the origin. What single rotation is this equivalent to?
A.90° clockwise rotation about the origin
B.270° counterclockwise rotation about the origin
C.90° counterclockwise rotation about the origin
D.360° rotation about the origin
Challenging
The final image of a vertex is A''(6, -2) after the composition (Reflection across y=x) ∘ (Rotation 90° CCW about origin). What were the coordinates of the original vertex A?
A.(6, 2)
B.(-2, -6)
C.(2, 6)
D.(-6, -2)
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