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8-6 Classifying Triangles
Warm Up
Problem of the Day
Lesson Presentation
Lesson Quizzes
8-6 Classifying Triangles
Warm Up
1. What is the name of a six-sided figure?
hexagon
2. What is the definition of an acute angle?
an angle that measures less than 90°
3. The measure of one of two
supplementary angles is 32°. What is the
measure of the other angle?
148°
8-6 Classifying Triangles
Problem of the Day
Use 6 congruent line segments to form 4
equilateral triangles. (Hint: Use
toothpicks or other objects to model the
segments.)
Place the segments so they form a
pyramid.
8-6 Classifying Triangles
Learn to classify triangles by their side
lengths and angle measures.
8-6 Classifying Triangles
Vocabulary
scalene triangle
isosceles triangle
equilateral triangle
acute triangle
obtuse triangle
right triangle
8-6 Classifying Triangles
One way to classify triangles is by the lengths of
their sides.
Triangles classified by sides
A scalene triangle
has no congruent sides.
8-6 Classifying Triangles
One way to classify triangles is by the lengths of
their sides.
Triangles classified by sides
An isosceles triangle
has at least 2 congruent sides
8-6 Classifying Triangles
One way to classify triangles is by the lengths of
their sides.
Triangles classified by sides
In an equilateral triangle, all of the
sides are congruent.
8-6 Classifying Triangles
One way to classify triangles is by the lengths of
their sides. Another way is by the measures of
their angles.
Triangles classified by angles
In an acute triangle, all of the
angles are acute.
8-6 Classifying Triangles
One way to classify triangles is by the lengths of
their sides. Another way is by the measures of
their angles.
Triangles classified by angles
An obtuse triangle has
one obtuse angle.
8-6 Classifying Triangles
One way to classify triangles is by the lengths of
their sides. Another way is by the measures of
their angles.
Triangles classified by angles
A right triangle
has one right angle.
8-6 Classifying Triangles
Additional Example 1: Classifying Triangles
Classify each triangle according to its sides
and angles.
A. isosceles Two congruent sides
acute
Three acute angles
This is an isosceles acute triangle.
B. scalene
right
No congruent sides
One right angle
This is a scalene right triangle.
8-6 Classifying Triangles
Additional Example 1: Classifying Triangles
Classify each triangle according to its sides
and angles.
C. equilateral Three congruent sides
acute
Three acute angles
This is an equilateral acute triangle.
D. scalene
right
No congruent sides
One right angle
This is a scalene right triangle.
8-6 Classifying Triangles
Check It Out: Example 1
Classify each triangle according to its sides
and angles.
A. isosceles Two congruent sides
acute
One obtuse angle
This is an isosceles acute triangle.
B. isosceles
right
Two congruent sides
One right angle
This is an isosceles right triangle.
8-6 Classifying Triangles
Check It Out: Example 1
Classify each triangle according to its sides
and angles.
C. scalene
obtuse
No congruent sides
One angle exceeding 90°
This is a scalene obtuse triangle.
D. scalene
obtuse
No congruent sides
One angle exceeding 90°
This is a scalene obtuse triangle.
8-6 Classifying Triangles
Additional Example 2: Identifying Triangles
Identify the different types of triangles in the
figure, and determine how many of each there are.
Type
How many
Name
Scalene
2
ABD,
BCD
Isosceles
2
ACE,
ABC
Right
ABD,
BCD
Obtuse
2
1
Acute
1
ACE
ABC
8-6 Classifying Triangles
Check It Out: Example 2
Identify the different types of triangles in the
figure, and determine how many of each there
are. A
I
B
J
D
H
G
C
Type
Isosceles
F
How many
5
E
Name
DJA,
JDG
HJI,
BCD
DFE
Obtuse
2
DJA,
ADG
Acute
4
JDG,
JHI,
BCD,
DEF
8-6 Classifying Triangles
Lesson Quizzes
Standard Lesson Quiz
Lesson Quiz for Student Response Systems
8-6 Classifying Triangles
Lesson Quiz
Classify each triangle according to its sides and
angles.
1. 7 ft, 8 ft, 12 ft
2. 45°, 90°, 45°
scalene
right
3. 12, 9, 12 isosceles
4. 120°, 20°, 40°
obtuse
5. Identify the different types of triangles in the
figure and determine how many of each there are.
1 isosceles acute triangle, 1 equilateral
triangle, 1 scalene right triangle
8-6 Classifying Triangles
Lesson Quiz for Student Response Systems
1. Classify the triangle according to its sides.
9 ft, 16 ft, 9 ft
A. equilateral
B. isosceles
C. scalene
D. right
8-6 Classifying Triangles
Lesson Quiz for Student Response Systems
2. Classify the triangle according to its sides.
5 in., 8 in., 12 in.
A. equilateral
B. isosceles
C. scalene
D. right
8-6 Classifying Triangles
Lesson Quiz for Student Response Systems
3. Classify the triangle according to its angles.
45°, 105°, 30°
A. acute
B. obtuse
C. right
D. equilateral
8-6 Classifying Triangles
Lesson Quiz for Student Response Systems
4. Classify the triangle according to its angles.
27°, 90°, 63°
A. acute
B. obtuse
C. right
D. equilateral