Download 5.1 Classifying Triangles

5.1 Classifying Triangles
Classifying Triangles
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 _____
three noncollinear points
are connected by segments.
D
E
F
Each pair of segments forms an angle of the triangle.
The vertex of each angle is a vertex of the triangle.
Classifying Triangles
Triangles are named by the letters at their vertices.
ΔDEF is shown below.
Triangle DEF, written ______,
vertex
angle
D
The sides are: EF, FD, and DE.
The vertices are: D, E, and F.
E
side
F
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.
acute angles.
All triangles have at least two _____
right
obtuse or _____.
The third angle is either _____,
acute ______,
Classifying Triangles
acute
triangle
60°
Triangles
Classified by
Angles
obtuse
right
triangle
120°
triangle
17°
30°
80°
60°
43°
40°
3rd angle is
3rd angle is
3rd angle is
acute
_____
obtuse
______
right
____
Classifying Triangles
scalene
isosceles
equilateral
no
___
sides
congruent
at least two
__________
sides
congruent
all
___
sides
congruent
Triangles
Classified by
Sides
Classifying Triangles
The angle formed by
the congruent sides is called the
vertex angle
___________.
The two angles formed by
the base and one of the
congruent sides are called
base angles
___________.
The congruent sides
are called legs.
leg
leg
The side opposite the vertex
angle is called the _____.
base