Wikipedia Law of Sines Question

[Trenters4325]

At the Wikipedia page for Law of Sines, what is the "medial angle law" in the "Derivation" section near the end of the first paragraph beneath the "Full Proof" subtitle?

 

[JakeD]

At the Wikipedia page for Law of Sines, what is the "medial angle law" in the "Derivation" section near the end of the first paragraph beneath the "Full Proof" subtitle?

The medial angle law appears to me to be "Inscribed Angle = 1/2 Intercepted Arc" found here. In the diagram below it says angle BAC = 1/2 angle BOC.

This diagram is from the link given in the Wikipedia page. I think that link has a clearer proof.