You just learned about three rigid transformations: This type of transformation is often called coordinate geometry because of its connection back to the coordinate plane. Rotation 180° around the origin: T( x, y) = (- x, - y) In the example above, for a 180° rotation, the formula is: Some geometry lessons will connect back to algebra by describing the formula causing the translation. That's what makes the rotation a rotation of 90°. Also all the colored lines form 90° angles. Notice that all of the colored lines are the same distance from the center or rotation than than are from the point. The figure shown at the right is a rotation of 90° rotated around the center of rotation. Also, rotations are done counterclockwise! You can rotate your object at any degree measure, but 90° and 180° are two of the most common. Reflection over line y = x: T( x, y) = ( y, x)Ī rotation is a transformation that is performed by "spinning" the object around a fixed point known as the center of rotation. Reflection over y-axis: T(x, y) = (- x, y) Reflection over x-axis: T( x, y) = ( x, - y) In other words, the line of reflection is directly in the middle of both points.Įxamples of transformation geometry in the coordinate plane. The line of reflection is equidistant from both red points, blue points, and green points. Notice the colored vertices for each of the triangles. Let's look at two very common reflections: a horizontal reflection and a vertical reflection. The transformation for this example would be T( x, y) = ( x+5, y+3).Ī reflection is a "flip" of an object over a line. More advanced transformation geometry is done on the coordinate plane. In this case, the rule is "5 to the right and 3 up." You can also translate a pre-image to the left, down, or any combination of two of the four directions. The formal definition of a translation is "every point of the pre-image is moved the same distance in the same direction to form the image." Take a look at the picture below for some clarification.Įach translation follows a rule. The most basic transformation is the translation. Translations - Each Point is Moved the Same Way You can know how to slide a shape using the T ( a, b ) T ( − 10, 3 ) because the first value is always the x-axis.The original figure is called the pre-image the new (copied) picture is called the image of the transformation.Ī rigid transformation is one in which the pre-image and the image both have the exact same size and shape. To avoid confusion, the new image is indicated with a little prime stroke, like this: P′, and that point is pronounced “ P prime. Suppose you have Point P located at (3, 4). The original reference point for any figure or shape is presented with its coordinates, using the x-axis and y-axis system, (x,y). Reflection – exchanging all points of a shape or figure with their mirror image across a given line (like looking in a mirror) Stretch – a one-way or two-way change using an invariant line and a scale factor (as if the shape were rubber) Shear – a movement of all the shape’s points in one direction except for points on a given line (like a crate being collapsed) Rotation – turning the object around a given fixed pointĭilation – a decrease in scale (like a photocopy shrinkage)Įxpansion – an increase in scale (like a photocopy enlargement) Translation – moving the shape without any other change You can perform seven types of transformations on any shape or figure: Translations are the simplest transformation in geometry and are often the first step in performing other transformations on a figure or shape.įor example, you may find you want to translate and rotate a shape. an isometry) because it does not change the size or shape of the original figure. A translation is a rigid transformation (a.k.a.
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