A cyclic Quadrilateral is a special type of quadrilateral that can be inscribed inside of a Circle.

Cyclicquad.png

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Properties

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Common Cyclic Quadrilaterals

Ptolemy's Theorem

Ptolemy's Theorem states that

This theorem can be proved by drawing point

on

such that

From triangle similarity, we have that

and

Cross-multiplying and then adding both equations gives us

We know that

, so hence,

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