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Geometry - Ch. 4
Chapter 4 Vocabulary, Postulates, & Theorems
44
Mathematics
9th Grade
03/13/2013

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Term
4.1
acute triangle
Definition
3 acute angles
Term
equiangular triangle
Definition
3 congruent acute angles
Term
obtuse triangle
Definition
1 obtuse angle
Term
right triangle
Definition
1 right angle
Term
equilateral triangle
Definition
3 congruent sides
Term
isosceles triangle
Definition
scalene triangle
Term
scalene triangle
Definition
no congruent sides
Term
4.2
triangle sum theorem
Definition
The sum of the measures of the angles of a triangle is 180.
Term
auxiliary line
Definition
an extra line or segment drawn in a figure to help analyze geometric relationships
Term
exterior angles
Definition
angles formed by one side of a triangle and the extension of an adjacent side
Term
remote interior angles
Definition
the 2 angles not adjacent to the exterior angle; each exterior angle has 2
Term
exterior angle theorem
Definition
The measure of an exterior angle is equal to the sum of the measures of the two remote interior angles
Term
flow proof
Definition
uses statements written in boxes and arrows to show the logical progression of the argument
Term
corollary
Definition
theorem with a proof that follows as a direct result of another theorem
Term
corollary 4.1
Definition
the acute angles of a right triangle are complementary
Term
corollary 4.2
Definition
there can be at most one right or obtuse angle in a triangle
Term
4.3
congruent
Definition
two geometric figures that are exactly the same size and shape.
Term
congruent polygons
Definition
2 polygons in which all the parts of one polygon are congruent to the corresponding parts or matching parts of the other
Term
corresponding parts
Definition
parts of two geometric figures that are congruent
Term
definition of congruent polygons
Definition
two polygons are congruent if and only if their corresponding parts are congruent
Term
third angles theorem
Definition
if two angles of one triangle are congruent to two angles of a second triangle, then the third angles are congruent
Term
properties of triangle congruence
Definition
Reflexive:
▲ABC≅▲ABC
Symmetric:
If ▲ABC≅▲EFG, then ▲EFG≅▲ABC.
Transitive:
If ▲ABC≅▲EFG and ▲EFG≅JKL, then ▲ABC≅▲JKL.
Term
4.4
SSS Congruence
Definition
if three sides of one triangle are congruent to three sides of a second triangle, then the triangles are congruent.
Term
included angle
Definition
the angle made by two adjacent lines is the included angle of those lines
Term
SAS Congruence
Definition
if two sides and the included angle of one triangle are congruent to two sides and the included angle of a second triangle, then the triangles are congruent.
Term
4.5
included side
Definition
the side located between two consecutive angles of a polygon
Term
ASA congruence
Definition
if two angles and a third side of one triangle are congruent to two angles and the included side of another triangle, then the triangles are congruent.
Term
AAS congruence
Definition
if two angles and the nonincluded side of one triangle are congruent to the corresponding two angles and side of a second triangle, then the triangles are congruent.
Term
4.6
legs of an isosceles triangle
Definition
two congruent sides of an isosceles triangle
Term
vertex angle
Definition
the angle formed by the legs of an isosceles triangle
Term
base angles
Definition
two angles formed by the base and the two congruent sides of an isosceles triangle
Term
isosceles triangle theorem
Definition
if two sides of a triangle are congruent, then the angles opposite those sides are congruent
Term
converse of isosceles triangle theorem
Definition
if two angles of a triangle are congruent, then the sides opposite those angles are congruent.
Term
corollary 4.3
Definition
a triangle is equilateral if and only if it is equiangular
Term
corollary 4.4
Definition
each angle of an equilateral triangle measures 60
Term
4.7
transformation
Definition
operation that remaps an original geometric figure
Term
preimage
Definition
the original geometric figure in a transformation
Term
image
Definition
new geometric figure in a transformation
Term
congruence transformation
Definition
one in which the image may differ from that of the preimage, but the two figures remain congruent.
Term
isometry
Definition
see congruence transformation
Term
reflection
Definition
a flip over a line called the line of reflection. each point of the preimage and image are the same distance from the line of reflection.
Term
translation
Definition
a slide that moves all points of the original figure the same distance in the same direction
Term
rotation
Definition
rurn around a fixed point called the center of rotation, through a specific angle, and in a specific direction. Each point in the preimage and image are the same distance from the center of rotation.
Term
4.8
coordinate proof
Definition
use figures in the coordinate plane and algebra to prove geometric concepts
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