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#1
 Apply 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 practice
 Do problems 3 -6 in your book page 220
Types of transformations
 What 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#5
 Determine 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 practice
 Do problems 7 and 8 in your book page 220
Example#7
 Prove 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#8
 Prove 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 practice
 Do 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!!!