Trigonometry (from the greek Trigonon (τρίγωνον, triangle)
and Metron (μέτρον, measure): resolution of the triangle) is the part of
mathematics that studies triangles starting from their corners. The main task
of trigonometry, as well as reveals the etymology of the name, is to calculate
the measures that characterize the elements of a triangle (the sides, corners,
medians, etc.) starting from other measures already known (at least three, of
which at least a length), by means of special functions.

This task is referred
to as the resolution of the triangle. You can also make use of trigonometric
calculations in solving problems related to more complex geometric shapes, such
as polygons or solid geometrical figures, and in many other branches of mathematics.

Trigonometric functions (the most important of which are the
sine and cosine), introduced in this area, are also used independently from the
geometry, appearing in other fields of mathematics and its applications, for
example in connection with the function exponential or with vector operations.

For many centuries, trigonometry had his progress almost
exclusively the work of great astronomers and geographers. In fact, the
foundation of this science is due to Hipparchus and Ptolemy, both astronomers
and geographers that most mathematicians. Significant contributions were made
to this science by the Arabs, from the French Gersonides and later by
Copernicus and Tycho Brahe, aims to describe and predict ever more precisely
the celestial phenomena, also for a more accurate and convenient calculation of
longitudes and latitudes.