Fundamentals Of Trigonometry

Introduction:
Trigonometry is an important branch of mathematics. The word Trigonometry has been derived from three Greek words: Trei (three), Goni (angles) and Metron (measurement). Literally it means measurement of triangle.

Units Of Measures Of angles:
There are two commonly used measurements for angles:

• Degrees
• Radians

Sexagesimal System: (Degree, Minutes, Seconds)
As this system of measurement of angle owes its origin to the English and because 90, 60 are multiples of 6 and 10, so it is known as English System or Sexagesimal System. 

1 rotation (anti-clockwise) = 360°

One degree ( 1° ) = 60'

One minute ( 1' ) = 60''

Circular System (Radians):

Radian is the measure of the angle subtended at the centre of the circle by an arc, whose length is equal to the radius of the circle.

1 radian = 180°∕π ≈180°∕3.1416 ≈ 57.296°