WEBVTT

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Here is the problem: A circle has radius 9. Find its radius, diameter, circumference and area.

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Find the radius, diameter, circumference and area of a circle from any one of them.

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Diameter.

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Circumference.

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Area.

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So the answer is r equals 9, d equals 18, C equals 18pi approximately 56.54866776, A equals 81pi approximately 254.4690049.

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Every measurement of a circle follows from its radius. The circumference grows in proportion to the radius and the area in proportion to its square.

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C/d equals 3.141592654 equals pi.

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A equals C times r/2 equals 254.4690049.