**Trigonometry** is a discipline of pure and applied mathematics which is used to study triangles and relationships between their sides and angles. Trigonometry describes these relationships and their applicability with the help of trigonometric functions to measure the objects in a space. The word Trigonometry is originated from the Greek Trigonon (triangle) a metron (measure). It is a part of middle and secondary school education and it taught as either a separate course or a pre-calculus curriculum.

Earlier trigonometry was developed by Hipparchus, who is known as ‘the father of trigonometry” as he prepared the first trigonometric table. Later his work was extended by ancient Greeks mathematicians, likewise modern sine function of trigonometry was defined in by an Indian mathematician and astronomer Aryabhatt in his book Surya Siddhanta in 5th century. In medieval time, Trigonometry was enriched by Persian and Islamic mathematicians and it was used to solve the problems in spherical geometry. Now it is an essential in various branches of science and technology including astronomy, navigation, and engineering.

Basically trigonometry is based on three angles and three lines of a triangle, which are calculated with the help of known angles or sides by using its six function including Sine, Cosine, Tangent, Cosine, Cosec Sine and their reciprocals cosecant (or cosec), secant (sec) and cotangent (cot) sine respectively. All the functions are calculated with the help of trigonometric tables.

Applications of trigonometry: trigonometric is a necessity for various branches of engineering and science and helps to locating positions of celestial objects in the given space. Its applications are widely used in astronomy, geography, satellite navigation, electronics, probability theory, statistics, medical imaging (as CAT scan and ultrasound), biology, chemistry, pharmacy, seismology, meteorology, oceanography, geodesy, civil engineering, architecture, economics, electrical engineering, computer graphics, cartography and crystallography.