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               The word trigonometry comes from the Greek words trigonon and mertron which means “triangle” and “to measure”. Until about 16 th century, trigonometry was chiefly concerned with computing the numerical values of the missing parts of a triangle, when the values of other parts were given.  Trigonometry in the modern sense began with the Greek astronomer, geographer and mathematician Hipparchus.  He was the first to construct a table of values for trigonometric functions.  As an astronomer, Hipparchus was mainly interested in spherical triangles, such as the imaginary triangle formed by three stars on the celestial sphere, but he was also familiar with the basic formulas of plane trigonometry.  Further development of trigonometry is from a need to compute angles and distances in such fields as astronomy, mapmaking, surveying, and artillery range finding. Problems involving angles and distances in one plane are covered in plane trigonometry. Applications to similar problems in more than one plane of three-dimensional space are considered in spherical trigonometry.