Review of Transformations Topic Index | Algebra2/Trig Index | Regents Exam Prep Center

Let's start with a review of transformations in the coordinate plane.
 

Remember that a reflection is simply a flip.  Under a reflection, the figure does not change size (it is an isometry).  It is simply flipped over the line of reflection.  The orientation (lettering of the diagram) is reversed.

Reflection in the x-axis:	When you reflect a point across the x-axis, the x-coordinate remains the same, but the y-coordinate is transformed into its opposite.      or     When working with the graph of , replace y with -y.
Reflection in the y-axis:	When you reflect a point across the y-axis, the y-coordinate remains the same, but the x-coordinate is transformed into its opposite.      or     When working with the graph of , replace x with -x.
Reflection in y = x:	When you reflect a point across the line y = x, the x-coordinate and the y-coordinate change places.        or
Reflection in y = -x:	When you reflect a point across the line y = -x, the x-coordinate and the y-coordinate change places and are negated (the signs are changed).     or

A point reflection exists when a figure is built around a single point called the center of the figure.  For every point in the figure, there is another point found directly opposite it on the other side of the center.  The figure does not change size (it is an isometry).

Reflection in the Origin:

While any point in the coordinate plane may be used as a point of reflection, the most commonly used point is the origin.     or    When working with the graph of , replace x with -x and y with -y.

A rotation turns a figure through an angle about a fixed point called the center.
The center of rotation is assumed to be the origin, unless stated otherwise.  A positive angle of rotation turns the figure counterclockwise, and a negative angle of rotation turns the figure in a clockwise direction.  The figure does not change size (it is an isometry).

Rotation of 90º:
Rotation of 180º:	(same as reflection in origin)
Rotation of 270º:

A dilation is a transformation that produces an image that is the same shape as the original, but is a different size (the figures are similar).  The description of a dilation includes the scale factor and the center of the dilation.   A dilation "shrinks" or "stretches" a figure (it is not an isometry).
 

Dilation of scale factor k:

The center of the dilation is assumed to be the origin unless otherwise specified.

A translation "slides" an object a fixed distance in a given direction.  The original object and its translation have the same shape and size (isometry), and they face in the same direction.

Translation of  h, k:

Under the image of  is  . If h > 0, the original graph is shifted h units to the right. If h < 0, the original graph is shifted units to the left. If k > 0, the original graph is shifted k units up. If k < 0, the original graph is shifted units down.