Objectives

• Classify triangles by angles. 
• Classify triangles by sides. 
• Draw specified triangles using a ruler and a protractor. 
• Find unknown angle measures in given triangles. 

Vocabulary

Triangle 

a three sided figure with three angles. The prefix “tri”means three. 

Acute Triangle 

all three angles are less than 90 degrees. 

Right Triangle 

One angle is equal to 90 degrees and the other two are acute angles. 

Obtuse Triangle 

One angle is greater than 90 degrees and the other two are acute angles. 

Equiangular Triangle 

all three angles are equal 

Scalene Triangle 

all three side lengths are different 

Isosceles Triangle 

two sides lengths are the same and one is different 

Equilateral Triangle 

all three side lengths are the same 

Protractor 

A tool used to measure angles 

Interior angles 

the angles inside a figure