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7-6 Triangles
Warm Up
Problem of the Day
Lesson Presentation
Course 2
7-6 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 angle of two
supplementary angles is 32°. What is the
measure of the other angle?
148°
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 make a
three-dimensional model with the
segments.)
Place the segments so they form a
pyramid.
Course 2
7-6 Triangles
Learn to classify triangles by their side
lengths and angle measures.
Course 2
7-6 Triangles
Insert Lesson Title Here
Vocabulary
scalene triangle
isosceles triangle
equilateral triangle
acute triangle
obtuse triangle
right triangle
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.
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
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.
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.
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.
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.
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.
Course 2
7-6 Triangles
Additional Example 1A & 1B: Classifying Triangles
Classify each triangle according to its sides
and angles.
A. isosceles Two congruent sides
acute
Three acute angles
5 ft
9 ft
9 ft
This is an isosceles acute triangle.
B. scalene
right
No congruent sides
One right angle
This is a scalene right triangle.
Course 2
24 m
25 m
7m
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.
Course 2
7-6 Insert
Lesson Title Here
Triangles
Try This: Example 1A & 1B
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
right
Two congruent sides
One right angle
This is an isosceles right triangle.
Course 2
5 ft
3 ft
3 ft
7-6 Insert
Lesson Title Here
Triangles
Try This: Example 1C & 1D
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.
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.
Course 2
Type
How many
Name
Scalene
2
ABD,
BCD
Isosceles
2
ACE,
ABC
Right
ABD,
BCD
Obtuse
2
1
Acute
1
ACE
ABC
7-6 Insert
Lesson Title Here
Triangles
Try This: 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
Course 2
C
Type
Isosceles
F
How many
5
E
Name
DJA,
JDG
HJI,
BCD
DFE
Obtuse
2
DJA,
ADG
Acute
4
JDG,
JHI,
BCD,
DEF
7-6 Triangles
Insert Lesson Title Here
Lesson Quiz
Classify each triangle according to its side or
angle measures.
1. 7ft, 8ft, 12ft scalene
2. 45°, 90°, 45° 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
Course 2