6th Grade Math Textbook, Fundamentals

 &KDSWHU

9-8

Key Concept

Classifying Triangles

Triangles can be classified by the lengths of their sides,

by the measures of their angles, and by both the lengths

of their sides and the measures of their angles

Triangles

Objective To classify triangles by angles, by sides, and by angles and sides

• To apply the concept of triangle inequality

Like the flags of several other countries, the flag of
Jamaica contains a few triangles. What kinds of
triangles do you see in this flag?

To find out, consider ways to classify triangles.

Triangles can be classified in three ways:

• By the measures of their angles;
  acute triangle
  three acute angles

obtuse triangle

one obtuse angle

right triangle

one right angle

scalene triangle

no sides congruent

• By the lengths of their sides;


• By both lengths of sides and measures of angles.

Remember:Matching tick marks indicate congruent sides.

acute scalene triangle

three acute angles

no congruent sides

obtuse isosceles triangle

one obtuse angle

two congruent sides

right scalene triangle

one right angle

no congruent sides

So there are two acute isosceles

triangles and two obtuse isosceles

triangles in the Jamaican flag.

Flag of Jamaica

equilateral triangle

all sides congruent

isosceles triangle

two sides congruent