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Dilations altoalsimce.org Topical synopsis | Geometry rundown | MathBits" Teacher resources Terms that Use call Person: Donna Roberts
For one intuitive evaluation of dilations, check out the Refresher section Transformations: Dilations. Now, let"s broaden that understanding of dilations in relationship to geometry.
A dilation is a transformation that produces picture that is the very same shape as the original, yet is a various size. The summary of a dilation has the scale factor (constant the dilation) and also the center of the dilation. The center of a dilation is a fixed allude in the plane about which every points are expanded or contracted. The facility is the just invariant (not changing) point under a dilation (k ≠1), and may be located inside, outside, or on a figure.

Note: A dilation is NOT referred to as a rigid transformation (or isometry) because the photo is no necessarily the exact same size together the pre-image (and strictly transformations keep length).

Referring come the diagram below:

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The dilation (centered at O with a scale variable of 2) that ΔABC = ΔA"B"C" making ΔABC ∼ ΔA"B"C" . This could also be written
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if you think about ΔABC to it is in the image.


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Dilations create comparable figures!
In this dilation, of scale aspect 2 mapping ΔABC to ΔA"B"C", the ranges from O come the vertices of ΔA"B"C" space twice the distances from O come ΔABC. after ~ a dilation, the pre-image and also image have the same shape however not the exact same size. Sides: In a dilation, the political parties of the pre-image and the equivalent sides of the image are proportional.

You are watching: A dilation is a transformation whose preimage and image are

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Properties maintained under a dilation from the pre-image to the image. 1. Angle measures (remain the same) 2. Parallelism (parallel lines stay parallel) 3. Collinearity (points continue to be on the exact same lines) 4. Orientation (lettering order remains the same) ---------------------------------------------------------- 5. Street is NOT
kept (lengths the segments are NOT the exact same in all instances except a scale variable of 1). A dilation is no a rigid change (isometry).
Scale Factor, k:

• If k > 1, enlargement. • If 0 • If k = 1, congruence. If k since sides of length 0 perform not exist, and division by 0 is no allowed, scale factors are never provided as zero (k ≠0).


ΔD"E"F" is the photo of ΔDEF (dilation facility O, scale factor ½).
Distances indigenous the center:
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A dilation is a transformation, DO,k , with facility O and a scale aspect of k that is no zero, the maps O come itself and any other allude P to P".
The facility O is a fixed point, P" is the image of P, clues O, P and also P" room collinear, and
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instance 1: k > 1 Enlargement Center of dilation O, scale element of 2.
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Case 2: 0 reduction Center that dilation O, scale element of ½.
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case 3: k = 1 Congruence Center of dilation O, scale aspect of 1.
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point P = allude P" (This one case can it is in classified together a rigid transformation.)
What happens as soon as scale factor k is a an unfavorable value? If the value of scale element k is negative, the dilation takes location in the opposite direction native the facility of dilation top top the very same straight line containing the center and the pre-image point. (This "opposite" placement may be described as gift a " command segment" since it has the building of being situated in a specific "direction" in relation to the center of dilation.)

situation 4: -1 Directed segment - reduction Center the dilation O, scale element of -½.
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(The an unfavorable symbol shows "direction", not negative length.)
Case 5: k Directed segments - Enlargement Center of dilation O, scale aspect of -2.
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Note: Consider that as soon as the absolute worth of the scale factor is better than 1, the photo will be larger thanthe pre-image. (When k
When the absolute value of the scale aspect is between 0 and also 1, the picture will be smaller than the pre-image. (When -1
Let"s see just how a negative dilation affects a triangle: an alert that the "image" triangles are on the opposite side of the center of the dilation (vertices are on opposite side of O from the preimage). Also notice that the triangles have actually been rotated 180º.

scale Factor: k = -½ palliation - Directed segment Center that dilation O, scale variable of -½
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range Factor: k = -1 Congruence - Directed segment Center of dilation O, scale factor of -1
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This dilation could likewise be expressed together a rotation of 180º focused at O.


Scale Factor: k = -2 Enlargement Directed segment Center the dilation O scale factor of -2
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did you notice the link between an unfavorable dilations and rotations? as soon as k = -1, the triangles are congruent and also the an adverse one scale aspect produces the exact same result as a rotation the 180º focused at O. We have the right to write:
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. This direct connection between dilations and rotations go NOT expand to dilations who scale determinants do no equal -1, such together the dilations that k = -½ and also k = -2. These dilations carry out not preserve length, and rotations must preserve length. We can, however, express these dilations as a composition the transformations including a rotation. Because that example, once k = -2, we can likewise describe that revolution as a dilation of scale factor +2 combined through a rotation that 180º (both focused at O). We can write:
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Dilations on coordinate Axis:

Dilation with facility at Origin, (0,0): The most famous dilation on a name: coordinates axis is a dilation centered at the origin. The majority of the dilation questions in Geometry are focused at the origin. Note that both the x and y coordinates are multiplied by the very same value, k.

Formula: center at Origin:

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O = facility of dilation in ~ (0,0); k = range factor


Given ΔDEF with facility of dilation the origin (0,0) and also scale factor of 2, plot ΔD"E"F". D(0,4), E(1,-2), and also F(-4,2)

As displayed in the formula above, multiply each x and also y coordinate value by the scale variable of 2 to uncover the brand-new coordinates.

D (0,4) i do not care D" (0,8) E (1,-2) i do not care E" (2,-4) F (-4,2) i do not care F" (-8,4)


Let the center (0,0) be labeled O:
Distance from center: OF" = 2OF OE" = 2OE OD" = 2OD
Length that Δ sides: F"D" = 2FD D"E" = 2DE F"E" = 2FE
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Dilation with center NOT in ~ Origin: A dilation ~ above a coordinate axis where the facility is not the origin deserve to be achieved by observing the vertical and horizontal distances of every vertex from the facility of dilation. In essence, we will be looking at the "slope" of every line (segment) involved.


Part 1: Given suggest C (-2,-1), facility of dilation the (-4,-9), and scale element of 2, find C".

By observation, point C is 8 upright units above the facility of dilation. Under a scale element of 2, allude C" needs to it is in 16 vertical units from the center.

Also, allude C is 2 horizontal units appropriate of the facility of dilation. Suggest C" needs to it is in 4 horizontal units ideal of the center.

Starting at the center of dilation (-4,-9), relocate 16 devices up and also 4 devices to the ideal to uncover C" in ~ (0,7).

NOTE: We are keeping the slope of the line passing with the center, suggest C, and allude C".


part 2: Plot the dilation of ΔABC by a scale factor of 2 through a facility of dilation in ~ (-4,-9). A(-4,-6), B(3,-6), and C(-2,-1)

By observing vertical and also horizontal distances from the facility of dilation, as seen in part 1, friend can find the remaining two collaborates of the dilated triangle.

A"(-4,-3), B"(10,-3), C"(0,7)


The counting of vertical and horizontal distances shown over is a basic and easy means to uncover the coordinates for a dilation not focused at the origin.

FYI: Another an approach A dilation not centered at the origin, can also be assumed of together a collection of translations, and also expressed as a formula. Translate the center of the dilation come the origin, use the dilation factor as presented in the "center in ~ origin" formula, then interpret the center earlier (undo the translation).

• first translate the center of the dilation for this reason the beginning becomes the center. Subtracting the coordinate values of the facility of dilation will relocate the facility to the origin. Given center of dilation at (a,b), interpret the facility to (0,0): (x - a, y - b). • Then apply the dilation factor, k: (k(x -a), k(y -b)) • and also translate back: (k(x - a) + a, k(y - b) + b)

Formula: center Not at Origin:

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O = center of dilation in ~ (a,b); k = scale aspect

write a coordinate rule to find the vertices of a dilation with facility (4,-2) and scale factor of 3.

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Let (x,y) it is in a vertex of the figure. Translate so the origin becomes center of the dilation (left 4 and up 2): (x - 4, y + 2). Apply the dilation formula when centered at origin: (3(x - 4), 3(y + 2)) = (3x - 12, 3y + 6) Translate earlier (right 4 and down 2): (3x - 12 + 4, 3y + 6 - 2) = (3x - 8, 3y + 4)

Rule: (x,y) → (3x - 8, 3y + 4)

For example, under this dilation, the point (5,6) becomes (3(5)-8, 3(6)+4) i m sorry is (7,22).


Topical rundown | Geometry overview | altoalsimce.org | MathBits" Teacher sources Terms of Use call Person: Donna Roberts