1. Classifying Triangles
Otherwise known as making triangles feel important by giving them hard to pronounce names

2. So what is classifying?
Basically it involves: (not a technical definition)
Observing a group of things
Putting them into groups with similar characteristics.

3. So let’s observe some triangles
This symbol means that this angle is a right angle which means it is 90°
What characteristics do all of these triangles have that we can use to classify them?
# of Sides
# of angles
Angles
Vertices
Side Length
So we will classify based on angles and side length
Not all of these are helpful since some characteristics are true of all triangles and won’t help us subdivide them
We can cross out the ones that all triangles have exactly the same
These symbols just represent the angle for that vertex

4. So let’s learn to classify by angle first…
When classifying by angle, you classify by the biggest angle in the triangle!!!
So I will be using the following angles to classify these triangles
Remember the 3 kinds of angles are:
Obtuse which is greater than 90°
Right which is equal to 90°
Acute which is less than 90°
These angles are all the same so we can use any

5. So let’s learn to classify by angle first…
Looking at the second triangle, it looks like our biggest angle would be exactly 90 °
Right
So this triangle would be….
So this triangle would be….
Looking at the first one, it looks like we would have all angles which are less than 90 °
Acute
Looking at the third triangle, it looks like our biggest angle would be more than 90 °
Obtuse
So this triangle would be….
Remember the 3 kinds of angles are:
Obtuse which is greater than 90°
Right which is equal to 90°
Acute which is less than 90°

6. Try these triangles by yourself. Classify them by angle
OBTUSE
OBTUSE
RIGHT
RIGHT
ACUTE
ACUTE
ACUTE

7. Brain Break

8. Now let’s learn to classify by side length
scalene
triangle
For this triangle no sides have the same length, so this is a…
There are 3 relationships that the sides can have with one another…
isosceles
triangle
For this triangle 2 sides have the same length, so this is an….
All 3 can be the same length which makes an equilateral triangle
2 sides can be the same length which makes an isosceles triangle
No sides are the same length which would make a scalene triangle
Try to determine what each of the triangles to the left are.
scalene
triangle
For this triangle no sides have the same length, so this is a…

9. Try to classify the following triangles by side length
All 3 can be the same length which makes an equilateral triangle
2 sides can be the same length which makes an isosceles triangle
No sides are the same length which would make a scalene triangle
Equilateral
Scalene
Isosceles
Scalene
Equilateral
Scalene
Scalene

10. You can also classify triangles by side and angle at the same time
Remember the 3 side length classifications are :
Equilateral: All sides are the same length
Isosceles: 2 sides are the same length
Scalene: No sides are the same length
This triangle has two sides that are the same, so it would an isosceles triangle. However, it’s biggest angle is less than 90° so it’s also acute.
So this triangle is an:
Acute isosceles triangle
or an
Isosceles acute triangle
Remember the 3 angle classifications are:
Obtuse which is greater than 90°
Right which is equal to 90°
Acute which is less than 90°

11. Try to classify the following triangles by angle and side length
Remember the 3 side length classifications are :
Equilateral: All sides are the same length
Isosceles: 2 sides are the same length
Scalene: No sides are the same length
Acute Equilateral
Obtuse Scalene
Acute Isosceles
Right Scalene
Remember the 3 angle classifications are:
Obtuse which is greater than 90°
Right which is equal to 90°
Acute which is less than 90°
Obtuse Isosceles
Right Scalene
Obtuse Scalene

12. Brain Break