Chapter 4 4-1 Congruence and transformations

SAT Problem of the day

Objectives Draw, identify, and describe transformations in

the coordinate plane. Use properties of rigid motions to determine

whether figures are congruent and to prove figures congruent.

Transformations What is a transformation?

Answer: is a change in the position, shape, or size of a figure.

What are some types of transformations?Answer: translations(slides),reflections,

rotations and dilations

Example#1Apply the transformation M to the polygon with

the given vertices. Identify and describe the transformation.

A. M: (x, y) → (x - 4, y + 1)P(1, 3), Q(1, 1), R(4, 1)

translation 4 units left and 1 unit up

Example#2

B. M: (x, y) → (x, -y) A(1, 2), B(4, 2), C(3, 1)

reflection across x-axis

Example#3. M: (x, y) → (y, -x) R(-3, 0), E(-3, 3), C(-1, 3), T(-1, 0)

90°rotation clockwise with center of rotation (0, 0)

Example#4. M: (x, y) → (3x, 3y) K(-2, -1), L(1, -1), N(1, -2))

dilation with scale factor 3 and center (0, 0)

Student guided practiceDo problems 3 -6 in your book page 220

Types of transformationsWhat is isometry ?An isometry is a transformation that preserves

length, angle measure, and area. Because of these properties, an isometry produces an image that is congruent to the preimage.

What is a rigid transformation?A rigid transformation is another name for an

isometry.

Transformations and congruence

Example#5Determine whether the polygons with the

given vertices are congruent.. A(-3, 1), B(2, 3), C(1, 1) P(-4, -2), Q(1, 0), R(0, -2)

The triangle are congruent; △ ABC can be mapped to △PQR by a translation: (x, y) → (x - 1, y - 3).

Example#6 B. A(2, -2), B(4, -2), C(4, -4) P(3, -3), Q(6, -3), R(6, -6).

The triangles are not congruent; △ ABC can be mapped to △ PQR by a dilation with scale factor k ≠ 1: (x, y) → (1.5x, 1.5y).

Student guided practiceDo problems 7 and 8 in your book page 220

Example#7Prove that the polygons with the given

vertices are congruent.A(1, 2), B(2, 1), C(4, 2)P(-3, -2), Q(-2, -1), R(-3, 1)

△ ABC can be mapped to △ A′B′C′ by a translation: (x, y) → (x – 3, y + 1); and then △ A′B′C′ can be mapped to △PQR by a rotation: (x, y) → (–y, x).

Example#8Prove that the polygons with the given

vertices are congruent: A(-4, -2), B(-2, 1), C( 2, -2) and P(1, 0), Q(3, -3), R(3, 0).

The triangles are congruent because ABC can be mapped to A’B’C’ by a translation (x, y) → (x + 5, y + 2); and then A’B’C’ can be mapped to ABC by a reflection across the x-axis

Student guided practiceDo problemsd9 and 10 in your book page 220

Architecture question?Is there another transformation that can

be used to create this frieze pattern? Explain your answer.

Repeated reflections can create this frieze pattern; a reflection of any section over a line through either the left or right side of each section.

Homework!!!Do problems even problems 13-24 in your

book page 220

Have a great day!!!