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tabulated the value of the chord function for every 7 1/2 degrees. In the 2nd century AD, Ptolemy compiled a more extensive table of chords in his book on astronomy, giving the value of the chord for angles ranging from 1/2 to 180 degrees by increments of 1/2 degree. Ptolemy used a circle of diameter 120, and gave chord lengths accurate to two sexagesimal (base

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