Heron's Formula and Ptolemy's Theorem

The goal of this article is to formalize some theorems that are in the [17] on the web. These are elementary theorems included in every handbook of Euclidean geometry and trigonometry: the law of cosines, the Heron's formula, the isosceles triangle theorem, the intersecting chords theorem and the Ptolemy's theorem.

MML identifier: EUCLID 6, version: 7.8.09 4.97.1001