Page 85 - Math Course 2 (Book 2)

Transformations: Rotated Images
Mo. 9

Lesson 4 angle of rotation

Angle of rotation is the measure of degrees that a
figure is rotated about a fixed point.

KEY CONCEPTS: B’ C’

1. Draw rotated images using the angle of
rotation. B
2. Identify figures with rotational symmetry. A’
angle of
0 x° rotation C

MO. 9 - L4a A
THEOREMS
Drawing Rotated Images
Theorem 9.1
In a given rotation, if A is the preimage, A’’ is the
image, and P is the center of rotation, then the
Vocabulary A-Z measure of the angle of rotation ∠APA’’ is twice the
measure of the acute or right angle formed by the
Let us learn some vocabulary intersecting line of reflection.
Corollary 9.1
rotation Reflecting an image successively in two
A rotation is a transformation that turns every perpendicular lines results in a 180° rotation.
point of a pre-image through a specified angle and
direction about a fixed point.

Let’s Begin
S
D’ A’

B’ D
Draw a Rotation
P’

A Example
C’
C P B
R Rotate quadrilateral RSTV 45° counterclockwise
about point A.
center of rotation
The fixed point is called the center of rotation.
S’
T’
S A’
D’
B’ D
V’ S
P’ R’

R is the A T
fixed point C’ R
C P B
R
m∠D’RD = 60 A V
m∠P’RP = 60
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