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Name _______________________________________ Date __________________ Class __________________ © Houghton Mifflin Harcourt Publishing Company Holt McDougal Analytic Geometry Reteach Congruence and Transformations TYPES OF TRANSFORMATIONS (centered at (0, 0)) Translation (slide): (x, y) (x a, y b) Reflection y-axis: (x, y) (x, y) x-axis: (x, y) (x, y) Rotation 90° clockwise: (x, y) (y, x) Dilation: (x, y) (kx, ky), k 0 Rotation 90° counterclockwise: (x, y) (y, x) Rotation 180°: (x, y) (x, y) Apply the transformation M to the polygon with the given vertices. Identify and describe the transformation. 1. M: (x, y) (x 1, y 2) A(1, 3), B(2, 2), C(2, 1) _____________________________________ 2. M: (x, y) (x, y) P(0, 0), Q(1, 3), R(3, 3) _____________________________________

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    Congruence and Transformations

    TYPES OF TRANSFORMATIONS (centered at (0, 0))

    Translation (slide): (x, y) (x a, y b) Reflection y-axis: (x, y) (x, y)

    x-axis: (x, y) (x, y)

    Rotation 90 clockwise: (x, y) (y, x) Dilation: (x, y) (kx, ky), k 0

    Rotation 90 counterclockwise: (x, y) (y, x)

    Rotation 180: (x, y) (x, y)

    Apply the transformation M to the polygon with the given vertices.

    Identify and describe the transformation.

    1. M: (x, y) (x 1, y 2)

    A(1, 3), B(2, 2), C(2, 1)

    _____________________________________

    2. M: (x, y) (x, y)

    P(0, 0), Q(1, 3), R(3, 3)

    _____________________________________

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    Congruence and Transformations continued

    An isometry is a transformation that preserves length, angle, and area. Because of these

    properties, isometries produce congruent images. A rigid transformation is another name for

    an isometry.

    Dilations with scale factor k 1 are transformations that produce images that are not

    congruent to their preimages.

    Determine whether the polygons with the given vertices are

    congruent.

    3. E(3, 1), F(2, 4), G(0, 0)

    H(1, 4), I(2, 1), J(4, 5)

    ___________________________________

    4. R(2, 4), S(0, 3), T(3, 1)

    U(2, 4), S(0, 3), V(3, 1)

    _____________________________________

    5. P(0, 0), Q(2, 2), R(2, 1)

    P(0, 0), S(4, 4), T(4, 2)

    _____________________________________

    6. J(2, 2), K(2, 1), L(1, 3)

    P(4, 4), Q(4, 2), R(2, 6)

    __________________________________________

    Transformation Isometry Image Preimage

    translation yes yes

    reflection yes yes

    rotation yes yes

    dilation no no

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    Angle Relationships in Triangles

    According to the Triangle Sum Theorem, the sum of the angle

    measures of a triangle is 1808.

    mJ mK mL 62 73 45

    1808

    The corollary below follows directly from the Triangle Sum Theorem.

    Use the figure for Exercises 1 and 2.

    1. Find mABC.

    __________________________________________

    2. Find mCAD.

    __________________________________________

    Use RST for Exercises 3 and 4.

    3. What is the value of x?

    __________________________________________

    4. What is the measure of each angle?

    __________________________________________

    What is the measure of each angle?

    5. L 6. C 7. W

    ________________________ ________________________ ________________________

    Corollary Example

    The acute angles of a right triangle are complementary.

    mC mE 908

    mC 90 39

    518

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    Angle Relationships in Triangles continued

    An exterior angle of a triangle is formed by

    one side of the triangle and the extension of

    an adjacent side.

    1 and 2 are the remote interior angles of

    4 because they are not adjacent to 4.

    Find each angle measure.

    8. mG 9. mD

    ________________________________________ ________________________________________

    Find each angle measure.

    10. mM and mQ 11. mT and mR

    ________________________________________ ________________________________________

    Exterior Angle Theorem

    The measure of an exterior angle of a

    triangle is equal to the sum of the

    measures of its remote interior angles.

    Third Angles Theorem

    If two angles of one triangle are congruent

    to two angles of another triangle, then

    the third pair of angles are congruent.

    m4m1 1 m2

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    Congruent Triangles Triangles are congruent if they have the same size and shape. Their corresponding parts,

    the angles and sides that are in the same positions, are congruent.

    To identify corresponding parts of congruent triangles, look at the order of the vertices in the

    congruence statement such as ABC JKL.

    Given: XYZ NPQ. Identify the congruent corresponding parts.

    1. Z ______________________ 2. YZ ______________________

    3. P ______________________ 4. X ______________________

    5. NQ ______________________ 6. PN ______________________

    Given: EFG RST. Find each value below.

    7. x ______________________ 8. y ______________________

    9. mF ______________________ 10. ST ______________________

    Corresponding Parts

    Congruent Angles Congruent Sides

    A J

    B K

    C

    L

    AB JK

    BC KL

    CA LJ

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    Congruent Triangles continued

    You can prove triangles congruent by

    using the definition of congruence.

    Given: D and B are right angles.

    DCE BCA

    C is the midpoint of .DB

    ,ED AB EC AC

    Prove: EDC ABC

    Proof:

    11. Complete the proof.

    Given: Q R

    P is the midpoint of .QR

    ,NQ SR NP SP

    Prove: NPQ SPR

    Statements Reasons

    1. D and B are rt. s . 1. Given

    2. D B 2. Rt.< Thm.

    3. DCE BCA 3. Given

    4. E A 4. Third s Thm.

    5. C is the midpoint of DB . 5. Given

    6. DC BC 6. Def. of mdpt.

    7. ,ED AB EC AC 7. Given

    8. EDC ABC 8. Def. of s

    Statements Reasons

    1. Q R 1. Given

    2. NPQ SPR 2. a. ____________________________

    3. N S 3. b. ____________________________

    4. P is the midpoint of .QR 4. c. ____________________________

    5. d. ____________________________ 5. Def. of mdpt.

    6. ,NQ SR NP SP 6. e. ____________________________

    7. NPQ SPR 7. f. ____________________________

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    Triangle Congruence: SSS and SAS

    You can use SSS to explain why FJH >

    FGH.

    It is given that FJ FG and that

    .JH GH By the Reflex.

    Prop. of , .FH FH So FJH FGH

    by SSS.

    Side-Side-Side (SSS) Congruence Postulate

    If three sides of one triangle are congruent to three sides of another triangle, then the triangles are congruent.

    , ,QR TU RP US and ,PQ ST so PQR STU.

    Side-Angle-Side (SAS) Congruence Postulate

    If two sides and the included angle of one triangle are congruent to two sides and the

    included angle of another triangle, then the triangles are congruent.

    Use SSS to explain why the triangles in each pair are congruent.

    1. JKM LKM 2. ABC CDA

    3.Use SAS to explain why WXY WZY.

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    Show that the triangles are congruent for

    the given value of the variable.

    You can show that two triangles are congruent by using SSS and SAS

    Show that JKL FGH for y 7

    HG y6 mG 5y5 FG 4y 1

    76 13 5(7)5 40 4(7) 1 27

    HG LK 13, so HG LK by def. of segs. mG40,

    so G K by def. of FG JK 27, so FG JK

    by def. of segs. Therefore JKL FGH by SAS.

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    Isosceles and Equilateral Triangles

    You can use these theorems to find angle

    measures in isosceles triangles.

    Find mE in DEF.

    mD mE Isosc. Thm.

    5x (3x14) Substitute the

    given values.

    2x 14 Subtract 3x from

    both sides.

    x 7 Divide both

    sides by 2.

    Thus mE 3(7)14 35.

    Find each angle

    measure.

    Theorem Examples

    Isosceles Triangle Theorem If two sides of a triangle are congruent, then the angles opposite the sides are congruent.

    If ,RT RS then

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    Isosceles and Equilateral Triangles continued

    Equilateral Triangle Corollary

    If a triangle is equilateral, then it is equiangular.

    (equilateral equiangular )

    Equiangular Triangle Corollary

    If a triangle is equiangular, then it is equilateral.

    (equiangular equilateral )

    If

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    Properties of Parallelograms

    A parallelogram is a quadrilateral with two pairs

    of parallel sides.

    All parallelograms, such as FGHJ, have

    the following properties.

    Properties of Parallelograms

    FG HJ

    GH JF

    Opposite sides are congruent.

    F H

    G J Opposite angles are congruent.

    mF mG 180

    mG mH 180

    mH mJ 180

    mJ mF 180 Consecutive angles are supplementary.

    FP HP

    GP JP

    The diagonals bisect each other.

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