Chapter 6
Lesson 6-5
Page 342
Key Idea
Triangles can be
classified according
to the lengths of
their sides or the
measures of
their angles.
Vocabulary
• equilateral
triangle
• isosceles triangle
• scalene triangle
• right triangle
• acute triangle
• obtuse triangle
Materials
• ruler or
straightedge
• protractor
• scissors
Classifying Triangles
How do you classify triangles?
Artists and architects
often use triangular
elements in their
designs. Classifying
triangles makes it
easier to describe
them.
Triangles can be classified by the lengths of their sides.
Equilateral triangle
All sides are
the same length.
Isosceles triangle
At least two sides
are the same length.
Scalene triangle
No sides are
the same length.
You can also classify triangles by the measures of their angles.
Right triangle
One angle is a
right angle.
Acute triangle
All three angles are
acute angles.
Obtuse triangle
One angle is an
obtuse angle.
Talk About It
1.
Can a right triangle also be isosceles? Explain.
2.
Which triangle appears to be a regular polygon? Explain.
3.
Classify all the angles in a right triangle and in an obtuse triangle.