Mathematics
Grade 10
15 min
Congruence transformations: mixed review (Tutorial Only)
Congruence transformations: mixed review (Tutorial Only)
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1
Introduction & Learning Objectives
Learning Objectives
Identify the specific translation, reflection, or rotation that maps a pre-image to its image.
Describe a sequence of two or more congruence transformations that maps one figure onto another.
Apply algebraic rules to determine the coordinates of an image after a sequence of transformations.
Write a coordinate rule for a given composition of congruence transformations.
Prove two figures are congruent by defining a sequence of rigid motions that maps one onto the other.
Differentiate between rigid motions (isometries) and non-rigid motions (like dilations).
Have you ever wondered how video game characters move across the screen without changing size or shape? 🎮 That's the magic of congruence transformations!
This tutorial is a comprehensive review of...
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Key Concepts & Vocabulary
TermDefinitionExample
Congruence Transformation (Isometry)A transformation that preserves distance, angle measure, and orientation. The pre-image (original figure) and the image (transformed figure) are congruent.Sliding a triangle 5 units to the right. The new triangle is identical in size and shape to the original.
TranslationA transformation that 'slides' every point of a figure the same distance in the same direction.Triangle ABC with vertices A(1,2), B(3,5), C(4,1) is translated 3 units right and 2 units down. The new vertices are A'(4,0), B'(6,3), C'(7,-1).
ReflectionA transformation that 'flips' a figure across a line, called the line of reflection, creating a mirror image.Reflecting the point P(2, 3) across the x-axis results in the image P'...
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Core Formulas
Translation Rule
T_{a,b}(x, y) = (x + a, y + b)
Use this to translate a point 'a' units horizontally and 'b' units vertically. If 'a' is positive, move right; negative, move left. If 'b' is positive, move up; negative, move down.
Reflection Rules
Across x-axis: R_{x-axis}(x, y) = (x, -y) \\ Across y-axis: R_{y-axis}(x, y) = (-x, y) \\ Across line y = x: R_{y=x}(x, y) = (y, x)
Use these rules to find the coordinates of a point after it has been reflected over a specific line. The most common lines of reflection are the axes and the line y=x.
Rotation Rules (about the origin)
90° counterclockwise: R_{90°}(x, y) = (-y, x) \\ 180°: R_{180°}(x, y) = (-x, -y) \\ 270° counterclockwise: R_{270°}(x, y) = (y, -x)
Use these rules for coun...
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Challenging
A reflection across the y-axis followed by a reflection across the x-axis is equivalent to which single transformation?
A.reflection across the line y = x
B.180° rotation about the origin
C.translation
D.90° counterclockwise rotation about the origin
Challenging
Write a single algebraic rule for the composition of a reflection across the line y = x, followed by a 90° counterclockwise rotation about the origin.
A.(x, y) -> (-x, y)
B.(x, y) -> (x, -y)
C.(x, y) -> (y, -x)
D.(x, y) -> (-y, -x)
Challenging
Triangle PQR has vertices P(6, 5), Q(8, 1), R(2, 1). Triangle S T U has vertices S(-5, 6), T(-1, 8), U(-1, 2). To prove ΔPQR ≅ ΔSTU, which sequence of rigid motions could be used to map ΔPQR onto ΔSTU?
A.translation 1 unit left and 11 units up.
B.reflection across the y-axis, followed by a translation.
C.180° rotation about the origin, followed by a translation.
D.90° counterclockwise rotation about the origin, followed by a translation.
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