# Introduction

The science of Trigonometry or "Three angles measurement" as we know it today is comparatively modern, but, like other branches of Mathematics, has its roots deep in the past. The Babylonians and Egyptians over 6000 years ago were interested in this angles measurement, mainly becasuse of their interest in the movement of stars and their journeys across the heaven. Before the sixteenth century, astronomy was based on the notion that the earth stood at the center of a series of nested spheres. To calculate the positions of stars or planets, we use trigonometry.

Aryabhatta

The study of Trigonometry was first started in India. The ancient Indian mathematician Aryabhatta, Brahmagupta and Bhaskara II got important results. All this knowledge went from here to middle - east and them to European countries. The aspect of Trigonometry was investigated by early Greeks, especially Hipparchus (180 - 125 B.C.)

Hipparchus (180 - 125 B.C.),the Greek astronomer is considered to be the 'father of astronomy' who was the first person to systematically survey the sky. He was the first to tabulate the corresponding values of arc and chord for a series of angles.His work was further developed by astronomers Menelaus and Ptolemy.

The early Babylonians divided the circle into 360 sectors,and thus gave us degrees, perhaps they thought that there were 360 days in a year. The sine function was invented in India around 300 - 400 A.D. By the end of 9th century, all the six trigonometric functions and the identities relating them were known to the Arabs.

The importance of Trigonometry needs no emphasis. It is used in surveying, navigation and all forms of earth and sky measurements. Currently Trigonometry is used in many areas such as the science of seismology, designing electric circuits, describing the state of an atom, predicting the heights of tides in an ocean, analyzing a musical tone, dynamics and statics (branches of physics). In short every subject and every branch of higher Mathematics requires a knowledge of Trigonometry.