1. an angle that measures less than 90°
Course 2
8-6
Classifying Triangles
Warm Up
1. What is the name of a six-sided figure?
2. What is the definition of an acute angle?
3. The measure of one of two supplementary angles is 32°. What is the measure of the other angle?
hexagon
an angle that measures less than 90°
148°

2. Classifying Triangles
Course 2
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 make a three-dimensional model with the segments.)
Place the segments so they form a pyramid.

3. Classifying Triangles
Course 2
8-6
Classifying Triangles
Learn to classify triangles by their side lengths and angle measures.

4. Insert Lesson Title Here
Course 2
8-6
Classifying Triangles
Insert Lesson Title Here
Vocabulary
scalene triangle
isosceles triangle
equilateral triangle
acute triangle
obtuse triangle
right triangle

5. Triangles classified by sides
Course 2
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.

6. Triangles classified by sides
Course 2
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

7. Triangles classified by sides
Course 2
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. Triangles classified by angles
Course 2
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.

9. Triangles classified by angles
Course 2
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.

10. Triangles classified by angles
Course 2
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.

11. Additional Example 1: Classifying Triangles
Course 2
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
No congruent sides
right
One right angle
This is a scalene right triangle.

12. Additional Example 1: Classifying Triangles
Course 2
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 a equilateral acute triangle. D.
scalene
No congruent sides
right
One right angle
This is a scalene right triangle.

13. Insert Lesson Title Here
Course 2
8-6
Classifying Triangles
Insert Lesson Title Here
Check It Out: Example 1
Classify each triangle according to its sides and angles. A.
isosceles
Two congruent sides
obtuse
One obtuse angle
This is an isosceles obtuse triangle. B.
isosceles
Two congruent sides
right
One right angle
This is an isosceles right triangle.

14. Insert Lesson Title Here
Course 2
8-6
Classifying Triangles
Insert Lesson Title Here
Check It Out: Example 1
Classify each triangle according to its sides and angles. C.
scalene
No congruent sides
obtuse
One angle exceeding 90°
This is a scalene obtuse triangle. D.
scalene
No congruent sides
obtuse
One angle exceeding 90°
This is a scalene obtuse triangle.

15. Additional Example 2: Identifying Triangles
Course 2
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 2
ABD,
BCD
Obtuse 1
ACE
Acute 1
ABC

16. Classifying Triangles Insert Lesson Title Here
Course 2
8-6
Classifying Triangles
Insert Lesson Title Here
Lesson Quiz
Classify each triangle according to its sides and angles.
1. 7ft, 8ft, 12ft
2. 45°, 90°, 45°
3. 12, 9, 12
4. 120°, 20°, 40°
5. Identify the different types of triangles in the figure and determine how many of each there are.
scalene
right
isosceles
obtuse
1 isosceles acute triangle, 1 equilateral triangle, 1 scalene right triangle