m708ct_c08_019B
3/7/07
3:31 PM
Page 19
SECTION
8B
Congruent Polygons
Lesson 8-6
Why? Congruence is used in many applications. For example, replacement parts in
machines must be congruent.
Congruent polygons are the
same shape and size. Their
corresponding sides and angles
have equal measures.
40°
P
R
U
82°
82°
58°
Q
PQR S
STU
58°
40°
T
You can find unknown values in congruent polygons.
If RQ x 8 and UT 20, then RQ UT.
RQ UT
x 8 20
x 12
Transformations
Lesson 8-7
Why? Transformations of, and symmetry in, geometric figures occurs often in art,
architecture, and engineering.
Translation
Reflection
Rotation
Center of
rotation
90° turn
180° turn
Line of symmetry
You can graph transformations on the coordinate plane.
y
Ī
{
Ī
{
ä
90° rotation
Þ
Þ
Ý
Ī
Ī
2
Ý
Ī ä
Ó
{
Ó
A translation 1 unit down
and 2 units right
Ī
Ī
A reflection across the x-axis
x
4
2
O
2
2
4
A counterclockwise rotation
about the origin