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4.1: Transformation

  • Page ID
    89852
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    4.1.1 Planar Transformations

    Definition: Transformation

    A function is a transformation if and only if it is one-to-one and onto.

    Definition: Planar Transformation

    A transformation is a planar transformation if and only if it is from ℝ2 to ℝ2.

    For this course all transformations will be transformations of the Euclidean plane.

    Describe the effect of each of the following transformations by considering the effects on the region (area) with the following vertices. (0,0), (2,0), (3,5), (0,4). Hint: map the vertices, then map the lines connecting the vertices.

    1. T1: (x, y) → (y, x).
    2. T2: (x, y) → (x/2, y/2).
    3. T3: (x, y) → (1-x3, 1-y3)
    4. T4: (x, y) → ((x2+y2)1/2x, (x2+y2)1/2y).

    4.1.2 Isometry

    Definition: Isometry

    A transformation is an isometry if and only if ll P - Q ll = ll T(P) - T(Q) ll.

    Determine which of the following transformations are isometries.

    1. T1: (x, y)→ (2x, 2y)
    2. T1: (x, y)→ (-y, -x)
    3. T1: (x, y)→ \(\begin{bmatrix} cosθ & sinθ \\ -sinθ & cosθ \end{bmatrix}\)\(\begin{bmatrix} x \\ y \end{bmatrix}\)
    Lemma

    The composition of two isometries is an isometry.

    Theorem: Isometries preserve colinearity

    For any isometry T if A, B and C are colinear, then T(A), T(B) and T(C) are colinear.

    Corollary: Isometries preserve betweeness

    For any isometry T if A-B-C then T(A)-T(B)-T(C).

    Theorem: Isometries preserve triangles

    For any isometry T and any three points △ABC ≌ △T(A)T(B)T(C).

    Theorem: Isometries preserve angles

    For any isometry T m∠ABC = m∠T(A)T(B)T(C) and any three points.

    Theorem: Isometries preserve parallelism

    For any isometry if T ℓ1 ll ℓ2 and only if T(ℓ1) ll T(ℓ2).

    Theorem: Isometries preserve circles

    For any isometry T circles are mapped to congruent circles.

    4.1.3 Dilations

    Definition: Dilation

    A transformation is a dilation if and only if it can be defined by a point Z and a ratio k such that T(P)=Q where Z-P-Q and llZQll/llZPll=k.

    Definition: Similarity

    A transformation is a similarity if and only if it can be expressed as a composition of an isometry and a dilation.

    Lemma: Similarity scales segments uniformly

    For any similarity T, llT(A)T(B)ll/llABll=k.

    Theorem: Similarity preserves colinearity

    For any similarity T if A, B, and C are colinear, then T(A), T(B), and T(C) are colinear.

    Corollary: Similarity preserves betweeness

    For any similarity T if then A-B-C then T(A)-T(B)-T(C).

    Theorem: Similarity preserves triangle similarity

    For any similarity T and any three points △ABC∽△T(A)T(B)T(C).

    Theorem: Similarity preserves angles

    T For any similarity and any three points ∠mABC∽ ∠ mT(A)T(B)T(C).

    Theorem: Similarity preserves parallelism

    For any similarity T ℓ1 ll ℓ2 if and only if T(ℓ1) ll T(ℓ2).

    Theorem

    For any similarity T circles are mapped to circles.

    Lemma: Similarities are closed

    The composition of two similarities is a similarity.


    This page titled 4.1: Transformation is shared under a GNU Free Documentation License 1.3 license and was authored, remixed, and/or curated by Mark A. Fitch via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.