Classifying Triangles

1
Classifying Triangles
What You'll Learn
You will learn to identify the parts of triangles
and to classify triangles by their parts.
In geometry, a triangle is a figure formed when
_____ noncollinear points are connected by
segments.
three
Each pair of segments forms an angle of the
triangle.
The vertex of each angle is a vertex of the
triangle.
2
Classifying Triangles
Triangles are named by the letters at their
vertices.
?DEF
Triangle DEF, written ______, is shown below.
The sides are
D, E, and F.
The vertices are
The angles are
?E, ?F, and ?D.
In Chapter 3, you classified angles as acute,
obtuse, or right.
Triangles can also be classified by their angles.
All triangles have at least two _____ angles.
acute
The third angle is either _____, ______, or _____.
obtuse
right
acute
3
Classifying Triangles
acute triangle
obtuse triangle
right triangle
3rd angle is _____
3rd angle is ______
3rd angle is ____
acute
obtuse
right
4
Classifying Triangles
scalene
isosceles
equilateral
no
at least two
all
___ sides congruent
__________ sides congruent
___ sides congruent
5
Classifying Triangles
vertex angle
The two angles formed by the base and one of
the congruent sides are called ___________.
The congruent sides are called legs.
base angles
leg
leg
The side opposite the vertex angle is called the
_____.
base
6
Classifying Triangles
Find x and BC if the given triangle is isosceles.
5x 7 23 5x 23 7 5x 30
x 6
A
5x-7
23
BC 3x 13 3(6) 13 18 13
31
B
C
3x13
7
Assignment
Page 190/ 3-19, 23, 26, 27, 29, 32, 35, 36