This document discusses classifying triangles by their angles and sides. It explains that triangles can be acute, obtuse or right depending on their angles. Acute triangles have all angles less than 90 degrees, obtuse triangles have one angle greater than 90 degrees, and right triangles have one 90 degree angle. Triangles can also be classified by their sides as equilateral, isosceles or scalene. Equilateral triangles have all three sides the same length, isosceles triangles have two sides the same length, and scalene triangles have all sides of different lengths. The document provides examples to illustrate each type of triangle classification.

1. Classifying
triangles by
angles and sides

2. Classifying by Angles
Right, Obtuse, and Acute

3. An acute triangle is a triangle whose angles
are all acute.
This is an acute triangle. What do you notice
about all three angles in this triangle?

4. An obtuse triangle has one obtuse angle.
Get out a sheet of paper and try to draw a
triangle with two obtuse angles.
This is an obtuse triangle. What do you
notice about this triangle?

5. This is a right triangle. What do you notice
about this triangle?
A right triangle is a triangle with a right
angle. Try to draw a triangle with two right
angles.

6. What kind of triangle is this?

7. What kind of triangle is this?

8. What kind of triangle is this?

9. Classifying by Sides
Equilateral, Isosceles, and Scalene

10. We have learned that you can name a
triangle by looking at its angles. Can you
name these three triangles?

11. Did you know that you
can name a triangle by
looking at its sides?
Click button to go to
BrainPop and view
“Types of Triangles,”
video clip.

12. Look at this triangle. What do you
notice about its sides?
All three sides are the same length
This is called an Equilateral Triangle.
How can you remember the name?

13. Look at this triangle. What do you
notice about its sides?
Two sides are the same length
This is called an Isosceles Triangle. Isos means
equal and skelos means leg. Put it together, and you
have a triangle with 2 equal legs!

14. This is called a Scalene Triangle. Scalene comes
from the word Skalenos, which means uneven or
unequal.
Look at this triangle. What do you
notice about its sides?
None of the sides are the
same length

15. Let’s see if we can sort
some triangles….