From the course: Test Prep: GRE
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Circle area and circumference
From the course: Test Prep: GRE
Circle area and circumference
- [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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Point, lines, segments, and planes1m 29s
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Angles2m 4s
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Parallel lines2m 19s
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Polygons2m 37s
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Triangles4m 2s
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Pythagorean theorem3m 11s
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Special right triangles3m 51s
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Area of a triangle2m 30s
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Congruent triangles2m 17s
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Similar triangles2m 40s
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Quadrilaterals4m 30s
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Circles3m 6s
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Circle area and circumference4m 10s
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Boxes5m 1s
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Cylinders3m 26s
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