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Circles Intro and Terminology

In geometry, a circle is a simple shape of two-dimensional Euclidean space that is the set of all points in a plane that are at a given distance from a given point, the centre.


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Video Transcript

Hi, Mr Clambered back with you today to talk about circles and some important vocabulary words related to circles. Let's first talk about what a circle is. We're all familiar with shape. It's all around us. But what is, by definition, a circle? Well, a circle is the set of all points in a plane, so it's plainer, which means it's two dimensional, the set of all points in a plane that air the same distance away from a given point. That same distance is referring to what we call on what you know as the radius, that point that they're all equally distant from we know as the center. So again, the definition is all the points in a plane, the same distance away. You might see it as a fixed distance away from a given point, which we call the center. Now that radius value we typically denote with our and if you go from one end of the circle through the center to the other end of the circle, you're probably familiar with that word as well. That is our diameter, which we denote D or you can also call it to our since it's twice the length of the radius. Now we often name a circle by its center. So, for example, if I have a circle, we have it center labeled as C and I will call this circle. See the capital letter. You're the special. Important terms and related terminology is that if you have a segment that goes from one part of the circle to another part of the circle that's known as a chord C H o R D. Now all of the cords that I'll draw here in a second are known as minor chords because they do not cross through the center of the circle. So there's a minor chord. There's a minor chord and so forth. If the court goes through the center of the circle, we call that a major chord. You might be thinking. Isn't that just the same thing as a diameter? And it iss okay, so a fancy name for the diameter is a major court. Alright, A few other things. If you have a circle and from its center, you create an angle. This is known as a central angle. Okay, because it's an angle that comes from the center of the circle and again. We could name it with three letters. We could call this angle ABC. We could call it angle C B A. But I couldn't call angle be because technically, there's two angles through the angle I've labeled, and then the larger angle that makes up the rest of the circle. So you have to name it via three letters if you have a circle again. But this time you have a point on the circle and you create an angle. From there, this angle is known as an inscribed angle, and again we called Angle A B C C B A. In this case, you could call angle be because there is only one angle emanating from Vertex. Be now what's created when we have these angles as you actually create divisions of the circle, now the entire distance around the circle that's known as the circumference, and that's kinda like the perimeter of the circle. But if we have this a chunk of the circumference like this part, for example, or this part, for example, we call these things arcs. Arcs are pieces of the entire circumference, and if the arcs are larger than half the circle, we call the major arcs if there are less than half the circle we call the minor arcs. So, for example, these two that I haven't read I would call minor arcs. And this one here, from this point all the way around to this point, I would call a major arc. How do you name marks? Well, two letters or three letters are used to to denote arcs. So encircle P Let's say, have this angle here and this angle here and this is a and this is B. The problem with calling it arc a B is that I'm not so sure if you mean the minor arc or the major ark, I'm not so sure if you mean that arc or this arc. So if you said minor arc baby, then I would know which. When you're talking about. Otherwise, you have the same major arc referring to the other RGB or if there was a point in between, you can say arc a let's call the C. And now I know you're talking about the arc from a to C to be so you can either name an arc by two letters with the arc symbol above but you have to make sure you indicated its minor or major. Or if it's ambiguous, please make sure that at another point, and then you can call it with three letters. And now the direction is established and you know how to call it by its appropriate name. So again, here's a rough, um, rough definition of what a circle is, and some terminology related to what circles are, and we'll be back with some examples.