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Honors Geometry Transformations Section 1 Reflections

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A transformation is a movement of a figure in a plane from its original position to a new position.

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The original figure is called the, while the figure resulting from the transformation is called the. A point in the image is usually named by adding a prime symbol ( ) to the name of the point in the preimage. preimage image

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In a rigid transformation, or isometry, the image is congruent to the preimage.

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We will consider three basic isometries: translations, reflections and rotations.

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A reflection in a line m (or flip over line m) is a transformation that maps (or matches up) any point P to a point so that these two properties are true. 1. If P is not on m, then 2. If P is on m, then

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Let’s take a look at reflections in the coordinate plane.

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Example 1: Consider reflecting point A(3, 5) in the given line. Give the coordinate of its image. A a) x-axis ________ b) y-axis ________ c) the line y = 1 _______ d) the line x = -2 ________

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e) the line y = x _______ f) the line y=-x+2 _____ g) the line y = x - 1 _____

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A figure has a line of symmetry if the figure can be mapped onto itself by a reflection in a line.

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The previous statement is the formal definition of a line of symmetry, but it is much easier to think of a line of symmetry as the line where the figure can be folded and have the two halves match exactly.

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Example 2: Draw all lines of symmetry.

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Example 3: Name two capital letters that have exactly two lines of symmetry.

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