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### Course: Basic geometry and measurement>Unit 3

Lesson 4: Understanding angle measurement

# Measuring angles with a circular protractor

Lindsay measures angles with a circular protractor.

## Want to join the conversation?

• Around the voiceover says you can go up to 360 degrees in an angle. I don't see 360 degrees on the protractor though. So, if it starts at 0 degrees will it end at 0 degrees to make a 360 degree angle? Sorry if I made that question confusing.
• You're right, both legs of a 360 degree angle would be in line with each other, same as with a 0 degree angle. The difference is that you're starting at 0 and measuring all the way around the circle, instead of starting at 0 and moving the endpoint zero degrees.
It would be accurate for the protractor to have a 360 degree mark there, but it doesn't because you can figure out that it's the same position as zero, just as you've done. It's sort of like how a clock with minute markings doesn't have 60 minutes marked, only 0.
• So what their doing is Measure the angle in degrees. So here we have blue angle that we want to measure in degrees, and it's sitting on top of this circle. That circle is actually a protractor. Sometimes we see, and maybe what you're used to seeing, is protractors that are more semicircle shaped, something like this. And those semicircle protractors measure from zero to 180 degrees. Which is good, but a circle is even better. A full circle is better because an angle can measure up to 360 degrees. So a full circle allows us to measure and angle of any size, instead of only an angle up to 180 degrees. Now the way we're gonna measure this angle is the same way we would on a semicircle protractor. The first thing we wanna do is make sure one of our rays lines up to zero. So here's one of our rays, and it's lining up to zero on the protractor. So that's nice, it's already lined up for us. And then we're gonna measure the opening all the way to the other ray, to right here. And so if our angle only measured opened up this far, it would be a 10 degree angle. If let's say it opened to here, it would be a 50 degree angle. But our angle measures all the way to here, to the 160 de
• Can you use a semicircle protractor to measure up to 360 degrees?
• It is always possible to flip a semi-circle protractor.
• Are all angles in circles obtuse?
• No, technically circles don't have any angles, since it is a closed, curved line. An angle is never closed.
• Sal Khan invented Khan Academy.
• wait who is the person speaking in this vid the person is different
• imagine getting 275 assignments

(def not from someone that got 275 assignments