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Lesson 2: Angle introduction

# Acute, right, & obtuse angles

Acute angles measure less than 90 degrees.  Right angles measure 90 degrees.  Obtuse angles measure more than 90 degrees.  Learn about angles types and see examples of each. Created by Sal Khan.

## Want to join the conversation?

• How do I label a line straight a cross?
• A straight line is 180 degrees, or a "straight" angle. Since it continues forever in both directions, it can also be considered a line.
• is there a angle more than 360 degrees
• No, if you pass 360 degrees, the angles rolls over and starts at 0 again. So, if you had a supposed 365 degree angle, it would really just be a 5 degree angle
• Is 190 degrees still considered an obtuse angle?
• No it is not because obtuse angles are more than 90 degrees but less than 180. Degrees above 180 and under 360 are reflex angles. 190 degrees are more than 180 so we cannot call it an obtuse angle but we can call it as reflex.
• Can angles be larger than 360 degrees or do they keep going back to 0 degrees in a circle?
• In basic geometry, an angle is the "opening" between two rays. But if we talk about angles greater than 360 degrees, this cannot happen BETWEEN two rays.

It is possible to ROTATE one ray around an axis away from another ray so that it goes all the way around and meets the original ray (360 degrees) - then you could rotate it another 90 degrees to come up with a ROTATION of 450 degrees. Hope that makes sense!
• an acute angle measure less than 90 degrees. right angle measures 90 degrees. obtuse angle measures more than 90 degrees
• easy way to remember these acute a cute little angle right square in the middle and obtuse big angle
• how does a zero degree angle look like?
(1 vote)
• A zero degree angle can be thought of as two rays right on top of each other with the same endpoint. These two rays can be thought of as being the same ray.

Have a blessed, wonderful day!
• What is obtuse?
• an angle that is greater than 90 degrees and shorter than 180 degrees.
• Me: takes a screenshot
Me: “I’ll use this later in the quiz and exercises.