| Term | Definition |
|---|
| transformation | The movement of a figure in a plane from its original position, the preimage, to a new position, the image. |
| Pre-image | A shape that undergoes a transformation. |
| Image | A shape that results from the transformation of a figure known as the preimage. |
| Reflection | A transformation such that every point of the preimage may be connected to its image point by a segment that is perpendicular to the line that is the "mirror" of the reflection and has its midpoint on the mirror of the reflection. |
| Translation | A transformation in which every point of the preimage moves in the same direction by the same amount to form the image. |
| Similar figures | Two figures that have the same shape, but not necessarily the same size; The sides of the corresponding sides are proportional or all the angles are equal. |
| Dilation | A transformation in which every point P has an image point P' such that a line connecting the two points passes through a point O, know as the center of dilation, and OP'=k * OP, where k is the scale factor of the dilation. |
| Direction | The orientation of a vector generally indicated by an arrowhead. |
| Corresponding sides | Sides of a polygon that are matched up with sides of another polygon with the same number of sides. |
| Corresponding angles | Angles of a polygon that are matched up with angles of another polygon with the same number of angles. |
| Line of reflection | The mirror line for a flip. |
| Expansion | A dilation in which the preimage is enlarged in size. (scale factor is greater than 1) |
| Contraction | A dilation in which the preimage is reduced in size. (scale factor is less than 1) |
| Glide reflection | A combination of a translation and a reflection. |
| Perpendicular bisector | A line that is perpendicular to a segment at its midpoint. |
| Midpoint | The point that divides a segment into two congruent segments. |
| Proportion | A statement of the equality of two ratios. |
| Ratio | a is to b as c is to d |
| Rigid transformation | A transformation that does not change the size or shape of a figure. |
| Rotation | A transformation in which every point of the preimage is rotated by a given angle about a point. |
| Scale factor | In a transformation, the number by which the distance of the preimage from the center of dilation is multiplied to determine the distance of the image point from its center. |
| Vector | A mathematical quantity that has both magnitude (a numerical measure - distance) and direction. |
| Center of rotation | The point an object is rotated around. |
| Center of dilation | The point used in dilating an object. |
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