Common Core: HSG-CO.A.5
Composite Transformation Theorems
There is a connection between the three transformations:
reflections, translations and rotations.
Parallel Lines Theorem: A
composition of reflections across two parallel lines is a
translation. When a figure is reflected in two parallel lines, the
final image is a translation in the direction perpendicular to the
parallel lines and twice the distance between them.
The following diagram shows that a composition of reflections across two parallel lines is a
translation. Scroll down the page for more examples and solutions of reflections across parallel lines.
Intersecting Lines Theorem: A
composition of reflections across two intersecting lines is a
rotation. When a figure is reflected in two intersecting lines,
then the final image is a rotation of the figure about the point
of intersection of the reflecting lines through an angle twice the
angle between the intersecting lines.
The following diagram shows that a composition of reflections across two intersecting lines is a
rotation. Scroll down the page for more examples and solutions of reflections across intersecting lines.
Composition of Transformations (1)
Looking at composition of transformations - combining
transformations in a series. Specifically looking at glide
reflections: translation followed by reflection.
Composition of Transformations (2)
Looking at composition of transformations - combining
transformations in a series. Specifically looking at glide
reflections, reflection followed by rotation.
Composition of Transformations (3)
Composition Theorem: The
composition of two or more isometries is an isometry.
Reflections in Parallel lines Theorem: If
lines k and m are parallel then the reflection in line k followed
by a reflection in line m is the same as a translation.
Composition of Transformations (4)
Reflection in Intersecting lines Theorem:
If lines k and m intersect at point, P, then a reflection
in k followed by a reflection in m is the same as a rotation about
the point, P.
Transformational Geometry (Translations, Rotations, Reflections)
Defining transformations to match polygons
Apply Composition of Transformations
Glide Reflection: Transformation followed by reflection
Translation followed by rotation
Composition of Transformations
Reflections in Parallel Lines Theorem
Reflections in Intersecting Lines Theorem
Composite Transformations in Geometric Figures
This video discusses composite transformations and work through some
examples of how to do a composite transformation.
Reflecting in Parallel Lines
Reflect the blue triangle in the blue-green line to form the green
image. Reflect the green triangle in the green-red line to form
the red image. The red triangle, being reflected twice, is
oriented like the blue triangle.
Ignoring the green triangle, the result of the two reflections is
to translate the blue triangle to the red triangle through twice
the distance between the two mirror lines.
Reflecting in Intersecting Lines
Reflect the blue triangle in the blue-green line to form the green
image. Reflect the green triangle in the green-red line to form the
red image. The red triangle, being reflected twice, is oriented like
the blue triangle.
Ignoring the green triangle, the result of the two reflections is to
rotate the blue triangle to the red triangle about the intersection
of the two mirror lines through twice the angle between them.
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