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Chapter 9 Vocabulary
This is an alphabetical list of new vocabulary terms you will learn in Chapter 9.
Add this page to your math binder to review vocabulary at the end of the chapter.
Vocabulary Term
Lesson
(p. #)
9-1
(p. 471)
Definition/Description/Example
acute triangle
9-1
(p. 471)
A triangle having three acute angles
angle
9-1
(p. 470)
Two rays with a common endpoint form an angle
complementary
angles
9-3
(p. 480)
Two angles are complementary if the sum of their measures is 90°
congruent angles
9-3
(p. 479)
Angles with the same measure
congruent figures
9-7
(p. 502)
Figures that are the same shape and size
congruent segments
9-4
(p. 488)
Line segments that have the same length
acute angle
[uh-KYOOT]
[kuhn-GROO-uhnt]
an angle with a measure greater than 0° and less than 90°
A
C
corresponding sides
degree
[dih-GREE]
equilateral triangle
[e-kwuh-LA-tuh-rul]
isosceles triangle
[eye-SAH-suh-LEEZ]
9-7
(p. 503)
9-1
(p. 470)
9-4
(p. 488)
9-4
(p. 488)
B
D
__
__
AB is congruent to CD
The parts of congruent or similar figures that match
The most common unit of measure for angles.
A triangle having all three sides congruent and all three angles
congruent
A triangle in which at least two sides are congruent
Vocabulary Term
Lesson
(p. #)
9-4
(p. 488)
Definition/Description/Example
obtuse angle
9-1
(p. 471)
An angle that measures greater than 90ºbut less than 180º
obtuse triangle
9-4
(p. 486)
A triangle having one obtuse angle
parallelogram
9-5
(p. 495)
A quadrilateral that has both pairs of opposite sides congruent and
parallel
quadrilateral
9-5
(p. 494)
9-5
(p. 495)
A polygon with four sides
rhombus
9-5
(p. 494)
A parallelogram with all sides congruent.
right angle
9-1
(p. 471)
An angle that measures 90°
right triangle
9-4
(p. 486)
A triangle having one right angle
scalene triangle
9-4
(p. 488)
A triangle in which no sides are congruent
side
9-1
(p. 470)
9-7
(p. 502)
A ray that is part of an angle
line segment
[ahb-TOOS]
[KWAH-druh-LA-tuh-ruhl]
rectangle
[RAHM-buhs]
[SKAY-leen]
similar figures
A straight path between two endpoints.
A quadrilateral with opposite sides congruent and parallel and all
angles are right angles
Figures that have the same shape but different sizes
Vocabulary Term
Lesson
(p. #)
9-5
(p. 495)
Definition/Description/Example
straight angle
9-1
(p. 471)
An angle that measures exactly 180º
supplementary
angles
9-3
(p. 480)
Two angles are supplementary if the sum of their measures is 180º
trapezoid
9-5
(p. 495)
A quadrilateral with one pair of opposite sides parallel
tessellation
9-7
(p. 508)
A pattern formed by repeating figures that fit together without
gaps or overlaps.
vertex
9-1
(p. 470)
The common endpoint of the two rays that form an angle
vertical angles
9-3
(p. 479)
Nonadjacent angles formed by a pair of lines that intersect
square
A parallelogram with all sides congruent, all angles right angles, and
opposite sides parallel.
Angle 1 and Angle 2 are supplementary angles.
Angles 1 and 3 are equal; Angles 2 and 4 are equal.