Classifying Triangles 2 Ways

Types of Triangles

Classifying triangles by their sides and lengths

• Triangles have special names based on their side lengths and angle measures.

  
  

  
  

• When you classify triangles by their side lengths, you use the words equilateral, isosceles, and scalene.

Equilateral Triangle

• An equilateral triangle has 

  three equal sides.

• This is an example of a equilateral triangle.

Isosceles triangle

• An isosceles triangle has two equal sides.

• This is an example of an isosceles triangle.

Scalene Triangle

• A scalene triangle has no equal sides.

• This is an example of scalene triangle.

Multiple Choice

Which of these triangles is scalene?

Multiple Choice

Which of these triangles is equilateral?

Multiple Choice

Which of these triangles is isosceles?

Classifying triangles by angle measure

• When you classify triangles by their angle measures, you use the words acute, right, and obtuse.

  
  

• Let's find out what those words mean!

Right Triangle

• A right triangle has one angle.

• Right angles measure exactly 90°.

• This is an example of a right triangle.

• Notice that all of the angles add up to be 180 degrees.

• The angles in a triangle always add up to 180 degrees

Obtuse triangle

• An obtuse triangle has one obtuse angle.

• Obtuse angles measure more than 90°.

• This is an example of an obtuse triangle.

Acute triangle

• An acute triangle has three acute angles.

• Acute angles measure less than 90°.

• This is an example of an acute triangle.

• Notice that all of the angles add up to be 180 degrees.

Equiangular Triangle

• An equiangular triangle has 

  three angles with the same measure.

• This is an example of a equiangular triangle.

• An equiangular triangle will also be equilateral.

Multiple Choice

Which of these triangles is obtuse?

Multiple Choice

• acute

• obtuse

• right

Multiple Choice

What type of angle is shown?

• acute

• obtuse

• right

• straight

Multiple Choice

Which of these is a right triangle?

Multiple Choice

• acute

• obtuse

• right

Multiple Choice

• acute

• obtuse

• right

Classifying triangles two ways

• This is a right isosceles triangle.

• It has a right angle and two equal sides.

Multiple Select

Classify the triangle by sides and angles (choose two answers).

• Acute triangle

• Obtuse triangle

• Equilateral triangle

• Isosceles triangle

• Scalene triangle

Multiple Select

Classify the triangle by sides and angles (choose two answers).

• Right triangle

• Acute triangle

• Obtuse triangle

• Isosceles triangle

• Scalene triangle

Multiple Select

Classify this triangle by sides and angles (choose multiple answers).

• Equiangular triangle

• Obtuse triangle

• Equilateral triangle

• Isosceles triangle

• Equiangular triangle

Multiple Choice

Which of these is an acute triangle?

Multiple Select

Classify the triangle by both sides and angles (choose two answers).

• Right triangle

• Acute triangle

• Obtuse triangle

• Isosceles triangle

• Scalene triangle

Multiple Select

Classify the triangle by sides and angles (choose two answers).

• Right triangle

• Acute triangle

• Obtuse triangle

• Equilateral triangle

• Isosceles triangle

Multiple Choice

How many acute angles must an acute triangle have?

• 2

• 1

• 4

• 3

Multiple Choice

An angle whose measure is exactly 90 degrees.

• acute

• vertical

• right

• straight

Multiple Choice

• acute

• obtuse

• right

Multiple Choice

• equilateral

• isosceles

• scalene

Multiple Choice

• equilateral

• isosceles

• scalene

Multiple Select

Classify the triangle by sides and angles (choose two answers).

• Acute triangle

• Obtuse triangle

• Equilateral triangle

• Isosceles triangle

• Scalene triangle

Multiple Choice

An obtuse triangle will always have _____ obtuse angles.

• One

• Two

• Three

Multiple Choice

Judy bought a new tent for camping. The sides measure 4 ft by 3 ft by 4 ft. All angles are less than 90 degrees. Classify the triangle by its sides and angles.

• Isosceles, obtuse

• Scalene, right

• Equilateral, acute

• Isosceles, acute

Multiple Choice

A triangle's sides measure 15 inches by 10 inches by 8 inches. It has one angle that measures 120 degrees. Classify the triangle by its sides and angles.

• Right, isosceles

• Equilateral, acute

• Obtuse, scalene

• Scalene, right