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Circle area and circumference

Circle area and circumference

From the course: Test Prep: GRE

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Circle area and circumference

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- [Voiceover] So a lot of times when we see circles in GRE geometry problems, we're gonna be dealing with their areas, or their circumferences, or maybe both. So let's talk about the formula for circle area first. So let's say we have a circle, and we know that its radius is three. So remember the radius is just a line drawn from the circle's center to any point on its edge. And there's a circle area formula that involves the circle's radius; It's just pi times the radius squared. So if we know the radius is three, then the area of that circle would be nine pi, 'cause we'll square three to get nine and multiply it by pi. Circumference has a formula as well; it's two pi r, where r, again, is the radius. So if we plug our radius, three, into this formula, we'll get three times two is six, and six pi. So a lot of people do get these formulas confused, so make sure that you study them enough so that they're second nature. You might remember that the squared formula is the one that…

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