# Classifying Triangles by Angles

##
Basics on the topic
**Classifying Triangles by Angles**

Learn how to classify triangles by angles.

###
Transcript
**Classifying Triangles by Angles**

Nico and Nia are part of the space clean-up program. They are in charge of the floating triangle debris, and must recycle them based on their angles! Let's join in and learn all about classifying triangles by angles. Today, we will be learning how to classify triangles based on their angles. An angle is the space between two intersecting lines, shown by an arc like this! To sort triangles by their angles, it is important to know that all triangles have at least two angles that are less than ninety degrees, or acute angles. Once you identify the two acute angles, then you can look at the third angle. If the third angle is also less than ninety degrees, the triangle is an acute triangle. There is also a special type of acute triangle called an equiangular triangle where all the angles are sixty degrees. Equiangular means all angles are equal. With this type of triangle, if the third angle is exactly ninety degrees, the triangle is a right triangle. And with this type of triangle, if the third angle is greater than ninety degrees, the triangle is an obtuse triangle. It looks like we are ready to help Nico and Nia with the space cleanup! Here is the first triangle, let's classify it! First, let's identify the two acute angles. Now, let's look at the third angle. What type of triangle is this based on the third angle? It is a right triangle, because the third angle is a right angle. This one can go in the right triangle recycling container! Here is the next triangle, let's classify it! First, let's identify the acute angles. Wait, it looks like ALL the angles are acute angles. What does this mean? If all the angles of a triangle are acute angles, then it's an acute triangle. This one can go in the acute triangle recycling container! Let's help with the final triangle. Which two angles are the acute angles? These two angles are acute angles since they're less than ninety degrees. Based on the third angle, what type of triangle is this? The third angle is an obtuse angle, so it is an obtuse triangle. This one can go in the obtuse triangle recycling container. While Nico and Nia finish up their day, let's review. Remember, triangles can be classified based on their angles. First, identify the two acute angles. Then, look at the third angle. If the third angle is less than ninety degrees, it is an acute triangle. If the third angle is exactly ninety degrees, it is a right triangle. If the third angle is greater than ninety degrees, it is an obtuse triangle. "You know, I did see a cute triangle out there!" "That's not right, Nico. Don't be so obtuse!"