Classifying Triangles

Mary S. Marks

Objective

• Today we will classify triangles by their sides and their angles.

• Given two angles in a triangle, we will find the third angle.

What are triangles?

• Tell me what you know about triangles.

(Note to teacher: Ask students what they know about triangles. Students should come up three sides, three angles, three vertices.)

Classifying Triangles by their Sides

• Equilateral Triangles - all sides are congruent

• Isosceles Triangles - two sides are congruent

• Scalene Triangles - no sides are congruent

Classifying Triangles by their Angles

• Acute Triangles - have three acute angles

• Obtuse Triangles - have one obtuse angle

• Right Triangles - have one right angle

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Examples of triangles

Sum of the measures of the angles in a triangle

• What type of angle do the angles in the triangle form?

• How many degrees does this type of angle have?

•How many degrees does this type of angle have?

Finding the missing angle

• Two angles are given, find the measurement of the third angle

?? ?

Finding the missing angle

• Two angles are given, find the measurement of the third angle

??

Finding the missing angle

• Two angles are given, find the measurement of the third angle

??

Finding the missing angle

• Two angles are given, find the measurement of the third angle

? ?

What is a triangle?

Equilateral

Right

Isosceles

Triangles in the Real World