Mathematics
Grade 9
15 min
Identify reflections, rotations, and translations
Identify reflections, rotations, and translations
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1
Introduction & Learning Objectives
Learning Objectives
Define and differentiate between reflections, rotations, and translations.
Identify the type of rigid transformation that maps a pre-image to its image on a coordinate plane.
Determine the line of reflection (x-axis, y-axis, y=x) given a pre-image and its reflected image.
Identify the center (origin) and angle of rotation (90°, 180°, 270°) for a given rotated figure.
Describe a translation using coordinate notation, such as (x, y) -> (x + a, y + b).
Verify that reflections, rotations, and translations are isometries that preserve side lengths and angle measures.
Ever wonder how animators make a character walk across the screen or a logo is flipped to create a perfect mirror image? 🎮
This tutorial explores the three fundamental rigid transformations:...
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Key Concepts & Vocabulary
TermDefinitionExample
Rigid Transformation (Isometry)A transformation that changes the position of a figure without changing its size or shape. It preserves distances, angle measures, and collinearity.Sliding a triangle 5 units to the right. The new triangle is congruent to the original.
Pre-imageThe original figure before a transformation is applied.If triangle ABC is transformed, ABC is the pre-image.
ImageThe resulting figure after a transformation has been applied.If triangle ABC is transformed into triangle A'B'C', then A'B'C' is the image.
ReflectionA transformation that 'flips' a figure across a line, called the line of reflection, creating a mirror image. The orientation of the figure is reversed.Reflecting the point (3, 2) across the y-axis...
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Core Formulas
Translation Rule
(x, y) \rightarrow (x + a, y + b)
This rule describes a translation. Every point on the pre-image is moved 'a' units horizontally and 'b' units vertically. A positive 'a' means a shift right, negative is left. A positive 'b' means a shift up, negative is down.
Common Reflection Rules
Across x-axis: (x, y) \rightarrow (x, -y) \\ Across y-axis: (x, y) \rightarrow (-x, y) \\ Across line y=x: (x, y) \rightarrow (y, x)
These rules show how the coordinates of a point change when reflected over the x-axis, y-axis, or the line y=x. Notice which coordinate changes sign or position.
Rotation Rules about the Origin (0,0)
90° counter-clockwise: (x, y) \rightarrow (-y, x) \\ 180°: (x, y) \rightarrow (-x, -y) \\ 270° counter-c...
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Challenging
Point A(2, 5) is first reflected across the y-axis to create point A'. Then, A' is translated by the rule (x, y) → (x + 3, y - 4). What are the coordinates of the final image, A''?
A.(1, 1)
B.(-5, 1)
C.(5, 1)
D.(1, 9)
Challenging
A point Q' has coordinates (6, 4). It is the image of point Q after a 90° counter-clockwise rotation about the origin. What are the coordinates of the pre-image Q?
A.(-4, 6)
B.(4, -6)
C.(-6, -4)
D.(-6, 4)
Challenging
Which of the following transformation rules does NOT describe a rigid transformation (isometry)?
A.(x, y) → (y, x)
B.(x, y) → (x - 7, y + 2)
C.(x, y) → (2x, 2y)
D.(x, y) → (-x, -y)
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