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Chapter 8 – Transformations. Brian Doherty. Lesson 1 – Transformations. Transformation – A one-to-one correspondence between two sets of points. Isometry – A transformation that preserves distance and angle measure. Lesson 2 – Reflections.
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Chapter 8 – Transformations Brian Doherty
Lesson 1 – Transformations • Transformation – A one-to-one correspondence between two sets of points. • Isometry – A transformation that preserves distance and angle measure.
Lesson 2 – Reflections • Reflection – The reflection of point P through line l is P itself if P is on l. Otherwise, it is the point P’ such that l is the perpendicular bisector of PP’. • Translation – A transformation that is the composite of two successive reflections through parallel lines. • Rotation – A transformation that is the composite of two successive reflections through intersecting lines.
Construction 8 – To Reflect a Point through a Line • Let the point be P and the line be l. With P as center, draw an arc that intersects l in two points, A and B. With A and B as centers, draw two more arcs with the same radius as the first arc. The point in which they intersect, P’, is the reflection of P through l.
Lesson 3 – Isometries and Congruence • Congruent figures – Two figures are congruent if there is an isometry such that one figure is the image of the other. • Glide reflection – A transformation that is the composite of a translation and a reflection in a line parallel to the direction of the translation.
Lesson 4 – Transformations and Symmetry • Rotation symmetry – A figure has rotation symmetry with respect to a point iff it coincides with its rotation image through less than 360˚ about the point. • Reflection symmetry – A figure has reflection (line) symmetry with respect to a line iff it coincides with its reflection image through the line. • Translation symmetry – A pattern has translation symmetry if it coincides with a translation image.
Extra – Dilations • Image – The result of a transformation. • Dilation – A transformation in which the original figure and its image are similar. • Scale factor – In a dilation, the ratio of any length on the image to the corresponding length on the original. • Center of dilation – The point which does not move under a dilation.