| A | B |
|---|
| preimage | the original figure in a transformation |
| reflecting line or line of reflection | the line over which a preimage is reflected |
| transformation | a correspondence between two sets of points such that each point in the preimage set has a unique image and each point in the image set has exactly one preimage |
| preserved property | under a transformation a property which if present in a preimage is present in the image |
| Reflection Postulate | under a reflection there is a one to one correspondence between points and their images with collinearity betweenness distance and angle measures preserved |
| reflection image of a figure | the set of all reflection images of the points of the original figure |
| Figure Reflection Theorem | if a figure is determined by certain points then its reflection image is the corresponding figure determined by the reflection images of those points |
| orientation of a figure | the order of the designation of the vertices of a polygon in either clockwise or counterclockwise |
| distance between two parallel lines | the length of a segment perpendicular to the lines with an endpoint on each of the lines |
| translation or slide | the composite of two reflections over parallel lines |
| direction of translation | the direction given by the vector from any preimage point to its image point in a translation |
| magnitude of translation | the distance between any point and its image |
| Two-Reflection Theorem for Translations | if line m is parallel to line l the translation r m*r l has magnitude two times the distance between l and m in the direction from l to m |
| Two-Reflection Theorem for Rotations | if m intersects l the rotation r m* r l has center at the point of intersection of m and l and has magnitude twice the measure of the non-obtuse angle formed by these lines in the directions from l to m |
| vector | a quantity that has both magnitude and direction |
| initial point | the beginning point of a vector |
| terminal point | the end point of a vector |
| horizontal component | the first component in the ordered pair description of a vector indicating its magnitude along the x-axis of the coordinate plane |
| vertical component | the second component in the ordered pair description of a vector indicating its magnitude along the y axis of the coordinate plane |
| ordered-pair description of a vector | the description of a vector as an ordered pair with a horizontal component and a vertical component |
| isometry | a transformation that is a reflection or a composite of reflections |
| concurrent lines | two or more lines that have a point in common |
| glide reflection | the composite of a reflection and a translation parallel to the reflecting line |
| congruent figures | a figure F is congruent to a figure G if and only if G is the image of F under a reflection or a composite of reflections |
| congruence transformation | a transformation that is a reflection or composite of reflections |
| directly congruent | figures which are congruent and have the same orientation |
| oppositely congruent | figures which are congruent and have opposite orientation |
