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Lesson 1: Triangles

# Classifying triangles

Learn to categorize triangles as scalene, isosceles, equilateral, acute, right, or obtuse.  Created by Sal Khan.

## Want to join the conversation?

• A triangle cannot contain a reflex angle because the sum of all angles in a triangle is equal to 180 degrees. A reflex angle is equal to more than 180 degrees (by definition), so that means the other two angles will have a negative size.
• What if I had a isosceles triangle. Would it be a right angle?
• No, it can't be a right angle because it is not able to make an angle like that. It's no an eqaulateral.
• Why is an equilateral triangle part of an icoseles triangle.
• I've asked a question similar to that.
An equilateral triangle has all three sides equal, right?
But on the other hand, we have an isosceles triangle, and the requirements for that is to have ONLY two sides of equal length. That's why.
• To remember the names of the scalene, isosceles, and the equilateral triangles, think like this!
Scalene: I have no rules, I'm a scale! My weight are always different!
Isosceles: I am an I (eye) sosceles (Isosceles)
Equilateral: I'm always equal, I'm always fair!
• That is a very good way!
• can i get 10 votes pls and hi im a tringle jk
• Are all triangles 180 degrees, if they are acute or obtuse?
• Yes. All of the internal angles of a triangle equal 180 degrees.
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