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Area of a Triangle
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How Pi Is DerivedArea of a CircleArea of a SectorPerimeter of a SectorRadians

Wedges to rectangle

Start with radius and circumference

C = 2 pi r
rpi rrArea stays the samecircle edge = 2 pi rmany wedges, each height ralternate wedges into a stripbase is half the rim: pi rarea = base x heightA = pi r2

A circle has radius r. Its outside edge is the circumference, which is 2 pi r.