8-6 Classifying Triangles Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day Lesson Quizzes Lesson Quizzes.

8-6 Classifying Triangles

Warm UpWarm Up

Lesson PresentationLesson Presentation

Problem of the DayProblem of the Day

Lesson QuizzesLesson Quizzes


Warm Up1. 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°


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.


Learn to classify triangles by their side lengths and angle measures.


Vocabulary

scalene triangleisosceles triangleequilateral triangleacute triangleobtuse triangleright triangle


One way to classify triangles is by the lengths of their sides.

Triangles classified by sides

A scalene trianglehas no congruent sides.




An isosceles trianglehas at least 2 congruent sides




In an equilateral triangle, all of the sides are congruent.


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.




An obtuse triangle hasone obtuse angle.




A right triangle has one right angle.


Classify each triangle according to its sides and angles.

Additional Example 1: Classifying Triangles

A. Two congruent sidesacute Three acute angles

This is an isosceles acute triangle.

B. No congruent sidesright One right angle

This is a scalene right triangle.

isosceles

scalene



Additional Example 1: Classifying Triangles

C. Three congruent sides

acute Three acute angles

This is an equilateral acute triangle.

D. No congruent sides

right One right angle

This is a scalene right triangle.

equilateral

scalene


Check It Out: Example 1


A. Two congruent sidesacute One obtuse angle

This is an isosceles acute triangle.

B. Two congruent sides

right One right angle

This is an isosceles right triangle.

isosceles

isosceles




C. No congruent sidesobtuse One angle exceeding 90°

This is a scalene obtuse triangle.

D. No congruent sides

obtuse One angle exceeding 90°

This is a scalene obtuse triangle.

scalene

scalene


Identify the different types of triangles in the figure, and determine how many of each there are.

Additional Example 2: Identifying Triangles

NameHow manyType

Scalene 2 ABD, BCD

Isosceles

Right

Obtuse

Acute

ACE, ABC

ABD, BCD

ACE

ABC

2

2

1

1



A

BC

D

EF

G

H

I J

Identify the different types of triangles in the figure, and determine how many of each there are.

Isosceles

Obtuse

Acute

5

2

4

NameHow manyType

DJA, JDG

HJI, BCD

DFE

DJA, ADG

JDG, JHI,

BCD, DEF


Standard Lesson Quiz

Lesson Quizzes

Lesson Quiz for Student Response Systems


Lesson Quiz


1. 7 ft, 8 ft, 12 ft

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.

right

scalene

isosceles

obtuse

1 isosceles acute triangle, 1 equilateral triangle, 1 scalene right triangle


1. Classify the triangle according to its sides.9 ft, 16 ft, 9 ft

A. equilateral

B. isosceles

C. scalene

D. right



2. Classify the triangle according to its sides. 5 in., 8 in., 12 in.

A. equilateral

B. isosceles

C. scalene

D. right



3. Classify the triangle according to its angles. 45°, 105°, 30°

A. acute

B. obtuse

C. right

D. equilateral



4. Classify the triangle according to its angles. 27°, 90°, 63°

A. acute

B. obtuse

C. right

D. equilateral


8-6 Classifying Triangles Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day Lesson Quizzes Lesson Quizzes.

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