Use the central angle to take the same fraction of circumference or circle area.
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First lesson in this subject: Complete the angle sum
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For radius r, the circumference is 2πr and the area is πr². Circumference measures length around the boundary; area measures the enclosed surface in square units.
For r = 4, the circumference is 8π units and the area is 16π square units. The radius runs from the center to the circle, not all the way across it.
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First lesson in this subject: Complete the angle sum
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Practice · Compare circumferences, areas, arcs and sectors. Change the radius or angle to test your reasoning.
Book · Explore measurements, transformations, coordinates and geometric relationships through diagrams and worked examples.
Previous lesson · Connect triangle totals to interior angles and one complete exterior turn.
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