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Dilations starrkingschool.net Topical overview | Geometry rundown | MathBits" Teacher resources Terms the Use contact Person: Donna Roberts
For an intuitive evaluation of dilations, view the Refresher ar Transformations: Dilations. Now, let"s increase that understanding of dilations in relation to geometry.
A dilation is a revolution that produces photo that is the very same shape together the original, however is a various size. The description of a dilation consists of the scale variable (constant of dilation) and the facility of the dilation. The facility of a dilation is a fixed point in the plane around which every points are broadened or contracted. The facility is the only invariant (not changing) allude under a dilation (k ≠1), and may be located inside, outside, or ~ above a figure.

Note: A dilation is NOT referred to as a rigid revolution (or isometry) since the photo is not necessarily the very same size together the pre-image (and rigid transformations keep length).

Referring to the diagram below:

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The dilation (centered at O through a scale aspect of 2) that ΔABC = ΔA"B"C" making ΔABC ∼ ΔA"B"C" . This could also be created
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if you consider ΔABC to be the image.


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

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

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

• If k > 1, enlargement. • If 0 • If k = 1, congruence. If k due to the fact that sides of size 0 do not exist, and department by 0 is not allowed, scale components are never noted as zero (k ≠0).


ΔD"E"F" is the picture of ΔDEF (dilation center O, scale aspect ½).
Distances indigenous the center:
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A dilation is a transformation, DO,k , with facility O and also a scale factor of k the is not zero, the maps O to itself and also any other point P come P".
The center O is a fixed point, P" is the image of P, point out O, P and also P" are collinear, and also
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instance 1: k > 1 Enlargement Center the dilation O, scale aspect of 2.
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Case 2: 0 reduction Center of dilation O, scale aspect of ½.
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instance 3: k = 1 Congruence Center that dilation O, scale factor of 1.
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allude P = suggest P" (This one case can it is in classified as a strictly transformation.)
What happens once scale factor k is a negative value? If the value of scale variable k is negative, the dilation takes location in the contrary direction native the center of dilation top top the very same straight line containing the center and also the pre-image point. (This "opposite" placement may be referred to as gift a " command segment" because it has the building of being situated in a certain "direction" in relationship to the facility of dilation.)

situation 4: -1 Directed segment - palliation Center the dilation O, scale factor of -½.
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(The negative symbol shows "direction", not an adverse length.)
Case 5: k Directed segment - Enlargement Center the dilation O, scale factor of -2.
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Note: Consider that when the absolute value of the scale variable is higher than 1, the picture will be bigger thanthe pre-image. (When k
When the absolute worth of the scale variable is between 0 and also 1, the picture will be smaller than the pre-image. (When -1
Let"s see how a an adverse dilation affect a triangle: notice that the "image" triangles room 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 reduction - Directed segment Center that dilation O, scale factor of -½
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scale Factor: k = -1 Congruence - Directed segment Center the dilation O, scale variable of -1
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This dilation could additionally be expressed together a rotation of 180º centered at O.


Scale Factor: k = -2 Enlargement Directed segment Center of dilation O scale variable of -2
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go you notice the link between negative dilations and rotations? when k = -1, the triangles room congruent and the negative one scale element produces the precise same an outcome as a rotation the 180º centered at O. We have the right to write:
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. This direct connection in between dilations and also rotations walk NOT extend to dilations whose scale determinants do no equal -1, such together the dilations the k = -½ and k = -2. These dilations execute not maintain length, and rotations must maintain length. Us can, however, express these dilations together a composition of transformations involving a rotation. For example, once k = -2, us can likewise describe that transformation as a dilation that scale aspect +2 combined with a rotation of 180º (both centered at O). We can write:
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Dilations on name: coordinates Axis:

Dilation with center at Origin, (0,0): The most famous dilation top top a coordinate axis is a dilation focused at the origin. The majority of the dilation concerns in Geometry are focused at the origin. Note that both the x and y coordinates room multiplied by the exact same value, k.

Formula: center at Origin:

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O = facility of dilation at (0,0); k = scale factor


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

As shown in the formula above, multiply every x and y coordinate worth by the scale variable of 2 to find the new coordinates.

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


Let the center (0,0) be labeled O:
Distance native center: OF" = 2OF OE" = 2OE OD" = 2OD
Length the Δ sides: F"D" = 2FD D"E" = 2DE F"E" = 2FE
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Dilation with center NOT in ~ Origin: A dilation on a name: coordinates axis wherein the center is no the origin deserve to be completed by observing the vertical and also horizontal distances of every vertex indigenous the center of dilation. In essence, we will certainly be looking at the "slope" of every line (segment) involved.


Part 1: Given allude C (-2,-1), center of dilation the (-4,-9), and scale variable of 2, find C".

By observation, suggest C is 8 upright units over the center 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 best of the facility of dilation. Suggest C" demands to be 4 horizontal units ideal of the center.

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

NOTE: We are keeping the slope that the heat passing through the center, suggest C, and point C".


component 2: Plot the dilation the ΔABC by a scale aspect of 2 through a facility of dilation at (-4,-9). A(-4,-6), B(3,-6), and also C(-2,-1)

By observing vertical and horizontal ranges from the facility of dilation, as checked out in component 1, girlfriend can uncover the continuing to be two coordinates of the dilated triangle.

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


The counting of vertical and also horizontal distances shown over is a straightforward and easy means to find the collaborates for a dilation not centered at the origin.

FYI: Another technique A dilation not focused at the origin, can also be believed of together a series of translations, and expressed together a formula. Analyze the facility of the dilation to the origin, apply the dilation element as displayed in the "center in ~ origin" formula, then interpret the center earlier (undo the translation).

• first translate the center of the dilation therefore the origin becomes the center. Subtracting the coordinate worths of the center of dilation will relocate the center to the origin. Given center of dilation in ~ (a,b), analyze the facility to (0,0): (x - a, y - b). • Then use the dilation factor, k: (k(x -a), k(y -b)) • and translate back: (k(x - a) + a, k(y - b) + b)

Formula: center Not at Origin:

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O = facility of dilation in ~ (a,b); k = scale factor

create a coordinate dominion to discover the vertices that a dilation with center (4,-2) and also scale variable of 3.

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Let (x,y) it is in a peak of the figure. Analyze so the origin becomes facility of the dilation (left 4 and up 2): (x - 4, y + 2). Apply the dilation formula when focused at origin: (3(x - 4), 3(y + 2)) = (3x - 12, 3y + 6) Translate earlier (right 4 and also 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 allude (5,6) i do not care (3(5)-8, 3(6)+4) i beg your pardon is (7,22).


Topical rundown | Geometry outline | starrkingschool.net | MathBits" Teacher resources Terms that Use call Person: Donna Roberts