If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: वर्ग 7 (Foundation)>Unit 3

Lesson 2: Types of triangles

# Classifying triangles

The video explores how triangles are classified based on their sides and angles. It introduces the terms scalene, isosceles, and equilateral for side lengths, and acute, right, and obtuse for angles. It emphasizes that triangles can be categorized in multiple ways based on these characteristics. 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.
• 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!
• Good Quote
(1 vote)
• 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.
• Are all triangles 180 degrees, if they are acute or obtuse?
• Yes. All of the internal angles of a triangle equal 180 degrees.
• Um, the acute triangle at . All of it's sides add up to 175, not 180. I checked on google. 60+61+54=175.
• That's just because Sal didn't draw a perfect triangle with completely straight lines and stuff. In a proper triangle, all the angles would add up to 180 degrees.
(1 vote)
• What is a reflex angle? I've heard of it, and @ultrabaymax mentioned it. Maybe this is the wrong video to post this question on, but I'm really curious and I couldn't find any other videos on here that might match this question.
• Good question! A reflex angle is an angle measuring greater than 180 degrees but less than 360 degrees.

Have a blessed, wonderful day!
• An equilateral triangle has all three sides equal?
But on the other hand, we have an isosceles triangle, and the requirements for that is to have ONLY two sides of equal length.
• An equilateral triangle has all three sides equal?
But on the other hand, we have an isosceles triangle, and the requirements for that is to have ONLY two sides of equal length.
Answer: Yes, the requirement for an isosceles triangle is to only have TWO sides that are equal. (e.g, there is a triangle, two sides are 3cm, and one is 2cm. That is an isosceles triangle. An equilateral triangle would have all equal sides.).
• Can an obtuse angle be a right.
Can a acute be a right to.
What type of isosceles triangle can be an equilateral.
An isosceles triangle can not be an equilateral because equilateral have all sides the same,but isosceles only has two the same.
• An obtuse triangle cannot be a right triangle. A right triangle must have one angle equal to 90 degrees. All three of a triangle's angles always equal to 180 degrees, so, because 180-90=90, the remaining two angles of a right triangle must add up to 90, and therefore neither of those individual angles can be over 90 degrees, which is required for an obtuse triangle.

An acute triangle can't be a right triangle, as acute triangles require all angles to be under 90 degrees. A right triangle has to have one angle equal to 90 degrees.

All isosceles triangles are equilateral. The only requirement for an isosceles triangle is for at minimum 2 sides to be the same length. An isosceles triangle can have more than 2 sides of the same length, but not less. Equilateral triangles have 3 sides of equal length, meaning that they've already satisfied the conditions for an isosceles triangle.
• I do not understand this help! but thank you I am new.
• We can classify triangles using its sides or interior angles.

Sides:
- Equilateral (All sides equal)
- Isosceles (At least 2 sides equal)
- Scalene (No sides equal)

Interior Angles
- Right (1 Angle is 90 degree, i.e. Right angle)
- Obtuse (1 Angle is larger than 90 degree, i.e. Obtuse angle)
- Acute (No angle is larger than or equal to 90 degree)