Theorem 5.8c: The area of an {n/k} star inscribed in a circle of radius r is

nr2sin(180/n)cos(180k/n)sec(180(k-1)/n)

proof 5: Using Theorem 5.1a, we could get the area of the star to be

nrrk-1sin(180/n)

by taking the angle at O. Using Theorem 4.3, this becomes

nr2cos(180k/n)sec(180(k-1)/n)sin(180/n)

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Proof 1

Proof 2

Proof 3

Proof 4

Proof 6