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 :looks like the law of cosines to me. The Pythagorean theorem is explicitly used once, in the first part of the spoke length calculation formula. The c in c² comes from the second part of the spoke length calculation formula - and that is the law of cosines, I would say. Do you agree? No original work is permitted in wikipedia, so if you figure something out, you need to find where someone else did it (citation) before placing it in article space. Look for the sides and angle and you will find them.