 168 AD) expanded upon Hipparchus' "Chords in a Circle" in his "Almagest", or the "Mathematical Syntaxis".The Almagest is primarily a work on astronomy, and astronomy relies on trigonometry.Ptolemy's table of chords gives the lengths of chords of a circle of diameter 120 as a function of the number of degrees "n" in the corresponding arc of the circle, for "n" ranging from 1/2 to 180 by increments of 1/2.