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### Course: Geometry (FL B.E.S.T.)>Unit 8

Lesson 2: Arc measure

# Intro to arc measure

Sal introduces arc measure including that they must sum to 360, conventions of minor and major arcs, and a comparison to arc length.

## Want to join the conversation?

• at how do you know its 240 degrees? and how can you solve equations using these methods
• Think about what you just posted and revise it before I call your teacher
• If the arc measure is 180° then which would be the minor/major arc or there would be no minor or major arc
• Great question! I was actually curious about that myself and what I've found is that a major arc is always greater than 180° and the minor arc is always less than 180°.

This means that there would be no minor/major arc, but instead both halves of the circle would be called semicircles.

Hope this helps,
- Convenient Colleague
• Two points lying on a circle actually define two arcs. The shortest is called the 'minor arc' the longer one is called the 'major arc'.A Major arc is usually referred with three letters, and a minor arc is usually referred to with only two letters. Typically, if you don't specify which arc you mean, then most people will assume you mean the minor (shortest) arc. If there is a possibility of confusion, you should state which one you mean. in this video, Sal probably referred to the minor arc with three letters because he had a picture to clarify. if an angle is 180 degrees, then it is a major arc.
• I think Doug was asking what if there was no third point listed? I had the same thought.
• When an Arc is described as 2 letters, which type of an Arc?
When an Arc is described as 3 letters, which type of an Arc?
• 2 letters is a minor arc (less than 180 degrees) and 3 letters is a major arc (greater than 180 degrees)
• I am wondering, when I take the test, I do not know whether they want me to find the minor arc or, the minor arc subtracted from the circle(360 degrees)
Do you know how to tell what they want? Different in wording or something?
• As Sal says in the video at around , you would usually use two letters for a minor arc and three letters to describe a major arc. Hope this helps!
• Is a 180 degree central angle a major or minor angle? And if the major angle has only 2 letters how should you name it?
• It depends on how the angle is named so 180 degree would be major if it was named with 3 points using the example in the video measure ACB but it would be minor if it only used two letters example AB. If the angle only has two letters then it is not major it is minor. REMEMBER it is the number of letters - 3 for major 2 for minor.
• Why is the arc measure the same as the central angle if it it so much bigger than it
• The arc measure is just the measure of how much the arc is around the circle. It is literally the same thing as the central angle because they both describe the same thing.

The arc length is the length of the arc and it will the distance of the arc which is what you were probably thinking about.

Hope this helps,
- Convenient Colleague
• how would u write it if says arc AOB?
• There is no such thing as arc AOB because he is using O as the center of the circle. Throughout the video, he says AOB is an angle, so you could write an angle sign and AOB after it. To signify atc AB, you write the letters and draw an arc symbol above it. He does this at about .