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Lesson 2: Angle introduction

# Recognizing angles

Sal identifies acute, obtuse, and right angles in diagrams and pictures. Created by Sal Khan.

## Want to join the conversation?

• What are real world uses for being able to identify angles of objects?
• anything that's up and right perfectly is a right angle... if you crack an door open a little its a acute angle if you open a cabinet almost al the way its obtuse
• So obtuse angles will always be bigger than right angles?
• A right angle is exactly 90 degrees. An obtuse angle, on the other hand, measures more than 90 degrees but less than 180 degrees. So, an obtuse angle is always bigger.
• Um... are you going to finish dat cwosson?
• knock yourself out
(1 vote)
• This teaches us about important stuff we need to know about angles at 90 or higher. 🌱🌿 But one thing: How can you tell a obtuse angle from a acute angle?
(1 vote)
• An obtuse would be greater than 90 degrees but less than 180 degrees.
And an acute angle is less than 90 degrees and more than 0 degrees, I remember acute by small angles are "aCUTE"
• is it like eureka math
• What is angle that has more than 180 called?
• A reflex angle is more than 180 but less than 360.
• I really appreciate the creative imagery xD Thanks Sal!
• good to watch
lol
• How do you get rid of your parole officer?
• hi is geometry easy?

## Video transcript

Look at the diagram below, then answer the following question. What type of angle is the angle highlighted in the green below? So it looks like two anteaters going after an ant right over here. And this anteater is going straight down, or at least on my screen it looks like it's going straight down. And this anteater's going straight to the left. And so it looks like this one's going straight down, this one's going straight to left. It looks like this is a right angle or a 90-degree angle. And so if I have to pick between any of these, it looks most like a right angle. It looks like this is exactly going down, and this is going exactly to the left, that this is a 90-degree angle here. If this was an acute angle, then the angle between them would be smaller. So maybe this top one would be coming in from this direction right over here. If it was obtuse, this angle would be larger. So let's just check our answer and try to do a few more of these. Which of the angles labeled in the diagram below are acute angles? So just as a reminder, an acute angle is less than 90 degrees. So let's see, A and C both look larger than 90 degrees. But B and D both look less than 90 degrees. So I'll go with B and D are the acute angles here. Let's do another one of these. What type of angle is the angle highlighted in green below? Well, this angle is less than 90 degrees. If it was equal to 90 degrees, this thing would come out like this. So this is clearly less than 90 degrees. This is an acute angle. Let me just do one more. This is a lot of fun. Select a symbol from the drop-down menu to complete the following statement. Then answer the question below. Angle A is less than 90 degrees. What type of angle is angle A? So angle A, it's less than 90 degrees. So an angle less than 90 degrees is an acute angle. If it was exactly 90 degrees, it would be a right angle. If it was larger than 90 degrees, it would be an obtuse angle. So I will go with acute angle. And we got it right.