Explanation of Ptolemy's Theorem

Answer 1

If a quadrilateral has its vertices on a common circle, then if you multiply the digonals, it should come out the same as if you take one pair of opposite sides, multiply their lengths, do the same for the next pair, and then add them together.

Answer 2

Ptolemy's Theorem states that in a quadrilateral, the product of the two diagonals is equal to the sum of the products of the opposite sides. Mathematically, for a quadrilateral with sides a, b, c, d and diagonals e and f, the theorem is represented as: ef = ac + b*d.