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Dilations starrkingschool.net Topical Summary | Geomeattempt Synopsis | MathBits" Teacher Resources Terms of Use Contact Person: Donna Roberts
For an intuitive review of dilations, watch the Refresher area Transformations: Dilations. Now, let"s expand also that knowledge of dilations in relation to geomeattempt.
A dilation is a transformation that produces a photo that is the same shape as the original, but is a various size. The summary of a dilation has the range aspect (consistent of dilation) and also the center of the dilation. The center of a dilation is a addressed suggest in the airplane about which all points are expanded or contracted. The center is the only invariant (not changing) allude under a dilation (k ≠1), and might be situated inside, external, or on a figure.

Note: A dilation is NOT referred to as a rigid transformation (or isometry) bereason the picture is NOT necessarily the exact same size as the pre-photo (and also rigid transformations preserve length).

Referring to the diagram below:

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The dilation (centered at O through a scale element of 2) of ΔABC = ΔA"B"C" making ΔABC ∼ ΔA"B"C" . This might additionally be composed
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if you think about ΔABC to be the photo.


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Dilations produce comparable figures!
In this dilation, of range factor 2 mapping ΔABC to ΔA"B"C", the distances from O to the vertices of ΔA"B"C" are twice the distances from O to ΔABC. After a dilation, the pre-picture and also picture have actually the very same form yet not the exact same size. Sides: In a dilation, the sides of the pre-image and also the corresponding sides of the photo are proportional.

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

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Properties kept under a dilation from the pre-photo to the picture. 1. angle measures (remain the same) 2. parallelism (parallel lines remain parallel) 3. collinearity (points remajor on the exact same lines) 4. orientation (lettering order stays the same) ---------------------------------------------------------- 5. distance is NOT
kept (lengths of segments are NOT the exact same in all situations other than a scale factor of 1). A dilation is NOT a rigid transdevelopment (isometry).
Scale Factor, k:

• If k > 1, enlargement. • If 0 • If k = 1, congruence. If k Since sides of size 0 do not exist, and also department by 0 is not allowed, range determinants are never listed as zero (k ≠0).


ΔD"E"F" is the photo of ΔDEF (dilation center O, range variable ½).
Distances from the center:
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A dilation is a change, DO,k , with center O and also a scale variable of k that is not zero, that maps O to itself and any type of various other point P to P".
The center O is a addressed allude, P" is the photo of P, points O, P and P" are coldirect, and
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Case 1: k > 1 Enlargement Center of dilation O, range element of 2.
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Case 2: 0 Reduction Center of dilation O, range aspect of ½.
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Case 3: k = 1 Congruence Center of dilation O, range aspect of 1.
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suggest P = suggest P" (This one case can be classified as a rigid transformation.)
What happens once range factor k is an unfavorable value? If the worth of range factor k is negative, the dilation takes area in the oppowebsite direction from the center of dilation on the very same right line containing the facility and also the pre-picture allude. (This "opposite" placement may be referred to as being a " directed segment" given that it has actually the residential property of being situated in a specific "direction" in relation to the center of dilation.)

Case 4: -1 Directed Segments - Reduction Center of dilation O, scale aspect of -½.
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(The negative symbol indicates "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 value of the scale element is higher than 1, the image will be bigger thanthe pre-picture. (When k
When the absolute value of the scale variable is between 0 and also 1, the image will certainly be smaller than the pre-photo. (When -1
Let"s check out how a negative dilation affects a triangle: Notice 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 alert that the triangles have been rotated 180º.

Scale Factor: k = -½ Reduction - Directed Segments Center of dilation O, scale variable of -½
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Scale Factor: k = -1 Congruence - Directed Segments Center of dilation O, range aspect of -1
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This dilation might likewise be expressed as a rotation of 180º focused at O.


Scale Factor: k = -2 Enlargement Directed Segments Center of dilation O range variable of -2
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Did you notification the connection between negative dilations and also rotations? When k = -1, the triangles are congruent and the negative one scale element produces the precise exact same outcome as a rotation of 180º centered at O. We can write:
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. This direct connection in between dilations and rotations does NOT extfinish to dilations whose range components do NOT equal -1, such as the dilations of k = -½ and also k = -2. These dilations carry out not keep length, and rotations must keep length. We deserve to, however, express these dilations as a complace of transformations involving a rotation. For instance, when k = -2, we have the right to additionally define that transdevelopment as a dilation of range aspect +2 combined through a rotation of 180º (both focused at O). We deserve to write:
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Dilations on Coordinate Axis:

Dilation via Center at Origin, (0,0): The most renowned dilation on a coordinate axis is a dilation centered at the origin. The majority of the dilation inquiries in Geomeattempt are centered at the origin. Keep in mind that both the x and also y works with are multiplied by the SAME worth, k.

Formula: Center at Origin:

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


Given ΔDEF through center of dilation the beginning (0,0) and scale factor of 2, plot ΔD"E"F". D(0,4), E(1,-2), and F(-4,2)

As shown in the formula over, multiply each x and y coordinate worth by the scale element of 2 to find the new works with.

D (0,4) becomes D" (0,8) E (1,-2) becomes E" (2,-4) F (-4,2) becomes F" (-8,4)


Let the facility (0,0) be labeled O:
Distance from center: OF" = 2OF OE" = 2OE OD" = 2OD
Length of Δ sides: F"D" = 2FD D"E" = 2DE F"E" = 2FE
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Dilation via Center NOT at Origin: A dilation on a coordinate axis wbelow the facility is NOT the origin can be achieved by observing the vertical and also horizontal ranges of each vertex from the facility of dilation. In significance, we will certainly be looking at the "slope" of each line (segment) affiliated.


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

By observation, point C is 8 vertical units above the facility of dilation. Under a range aspect of 2, point C" demands to be 16 vertical units from the facility.

Also, suggest C is 2 horizontal systems best of the facility of dilation. Point C" requirements to be 4 horizontal devices ideal of the facility.

Starting at the center of dilation (-4,-9), move 16 units up and 4 units to the best to uncover C" at (0,7).

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


Part 2: Plot the dilation of ΔABC by a scale variable of 2 via a center of dilation at (-4,-9). A(-4,-6), B(3,-6), and also C(-2,-1)

By observing vertical and also horizontal distances from the center of dilation, as seen in Part 1, you deserve to find the continuing to be two collaborates of the dilated triangle.

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


The counting of vertical and also horizontal distances presented over is a simple and straightforward method to discover the coordinates for a dilation not focused at the beginning.

FYI: Another Method A dilation not centered at the beginning, can also be thought of as a collection of translations, and also expressed as a formula. Translate the center of the dilation to the origin, use the dilation factor as shown in the "facility at origin" formula, then interpret the center back (uncarry out the translation).

• First analyze the center of the dilation so the beginning becomes the center. Subtracting the coordinate values of the center of dilation will certainly move the center to the beginning. Given facility of dilation at (a,b), translate the center to (0,0): (x - a, y - b). • Then use the dilation element, 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 = center of dilation at (a,b); k = range factor

Write a coordinate ascendancy to uncover the vertices of a dilation with facility (4,-2) and also range element of 3.

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Let (x,y) be a vertex of the figure. Translate so the beginning becomes facility of the dilation (left 4 and up 2): (x - 4, y + 2). Apply the dilation formula once focused at origin: (3(x - 4), 3(y + 2)) = (3x - 12, 3y + 6) Translate ago (right 4 and dvery own 2): (3x - 12 + 4, 3y + 6 - 2) = (3x - 8, 3y + 4)

Rule: (x,y) → (3x - 8, 3y + 4)

For instance, under this dilation, the point (5,6) becomes (3(5)-8, 3(6)+4) which is (7,22).


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