1. 7-6
Triangles
Course 2
Warm Up
Problem of the Day
Lesson Presentation

2. an angle that measures less than 90°
Course 2
7-6
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 angle of two supplementary angles is 32°. What is the measure of the other angle?
hexagon
an angle that measures less than 90°
148°

3. 7-6 Triangles Problem of the Day
Course 2
7-6
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.

4. Course 2
7-6
Triangles
Learn to classify triangles by their side lengths and angle measures.

5. Insert Lesson Title Here
Course 2
7-6
Triangles
Insert Lesson Title Here
Vocabulary
scalene triangle
isosceles triangle
equilateral triangle
acute triangle
obtuse triangle
right triangle

6. Triangles classified by sides
Course 2
7-6
Triangles
One way to classify triangles is by the lengths of their sides.
Triangles classified by sides
A scalene triangle
has no congruent sides.

7. Triangles classified by sides
Course 2
7-6
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. Triangles classified by sides
Course 2
7-6
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.

9. Triangles classified by angles
Course 2
7-6
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.

10. Triangles classified by angles
Course 2
7-6
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.

11. Triangles classified by angles
Course 2
7-6
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.

12. Course 2
7-6
Triangles
Writing Math
When classifying a triangle according to its sides and angles, use the word that describes the sides first, and use the word that describes its angles second.

13. Additional Example 1A & 1B: Classifying Triangles
Course 2
7-6
Triangles
Additional Example 1A & 1B: Classifying Triangles
Classify each triangle according to its sides and angles.
5 ft A.
isosceles
Two congruent sides
9 ft
9 ft
acute
Three acute angles
This is an isosceles acute triangle. B.
scalene
No congruent sides
right
One right angle
24 m
25 m
This is a scalene right triangle.
7 m

14. Additional Example 1C & 1D: Classifying Triangles
Course 2
7-6
Triangles
Additional Example 1C & 1D: Classifying Triangles
Classify each triangle according to its sides and angles. C.
scalene
No congruent sides
acute
Three acute angles
This is a scalene acute triangle. D.
equilateral
Three congruent sides
acute
Three acute angles
This is an equilateral acute triangle.

15. Insert Lesson Title Here
Course 2
7-6
Triangles
Insert Lesson Title Here
Try This: Example 1A & 1B
Classify each triangle according to its sides and angles.
5 ft A.
isosceles
Two congruent sides
3 ft
3 ft
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.

16. Insert Lesson Title Here
Course 2
7-6
Triangles
Insert Lesson Title Here
Try This: Example 1C & 1D
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.

17. Additional Example 2: Identifying Triangles
Course 2
7-6
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

18. Insert Lesson Title Here
Course 2
7-6
Triangles
Insert Lesson Title Here
Try This: Example 2
Identify the different types of triangles in the figure, and determine how many of each there are. A I J B
Type
How many
Name C
DJA,
JDG
HJI,
BCD
DFE H D
Isosceles 5 F G E
DJA,
ADG 2
Obtuse
JDG,
JHI,
BCD,
DEF
Acute 4

19. Insert Lesson Title Here
Course 2
7-6
Triangles
Insert Lesson Title Here
Lesson Quiz
Classify each triangle according to its side or angle measures.
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