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Surface Area of Spheres

Drag the red point to see how a sphere can be dissected into n pyramids (approximate) of heights equal the radius r. Let A1, A2, ..., An be the base areas of the pyramids. (a) Show that 1/3 (A1+ A2 + ... + An) r ≈ Volume of the sphere (a) When n tends to infinity, show that 1/3 S r = V where V and S are the volume and surface area of the sphere respectively. Hence show that S = 4 π r² .