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Labeling parts of a circle

Radius, diameter, center, and circumference--all are parts of a circle. Let's go through each and understand how they are defined. Created by Sal Khan and Monterey Institute for Technology and Education.

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Video transcript

Draw a circle and label the radius, diameter, center, and the circumference. Let me draw a circle. And it won't be that well drawn of a circle, but I think you get the idea. So that is my circle. I'm going to label the center over here. I'll do the center. I'll call it c. So that is my center. And I'll draw an arrow there. That is the center of the circle. And actually, the circle itself is the set of all points that are a fixed distance away from that center. And that fixed distance away that they're all from that center, that is the radius. So let me draw the radius. So this distance right over here is the radius. That is the radius. And that's going to be the same as this distance, which is the same as that distance. I can draw multiple radii. All of these are radii, the distance between the center and any point on the circle. Now, a diameter just goes straight across the circle, going through the center. From one side of the circle to the other side, I'm going through the center. It's essentially two radii put together. So for example, this would be a diameter. You have one radii, than another radii, all one line, going from one side of the circle to the other, going through the center. So that is a diameter. And I could have drawn it other ways. I could've drawn it like this. That would be another diameter. But they're going to have the exact same length. And finally, we have to think about the circumference. And the circumference is really just how far you have to go to go around the circle. Or if you put a string on this circle, how long will that string have to be? So what I'm tracing out in blue right now, the length of what I'm tracing out, is the circumference. So right over here, that is the circumference. And we're done.