TRIGONOMETRY

TRIGONOMETRY BASIC EQUATIONS

 CHAPTER 3

 TRIGONOMETRIC FUNCTIONS

Angle

Angle is a measure of rotation of a given ray about its 

initial point.The original ray is called the initial side and 

the final position of the ray is called the terminal side 

of the angle. The point of rotation is called the vertex.

 

If the direction of rotation is anticlockwise,the angle is 

said to be positive.If the direction is clockwise then the 

angle is negative.

If the ray rotates and come to its original position,we 

say that it has completed one revolution.

Two units of measurement of an angle

1.Degree measure

If a rotation from the initial side to terminal side is 

(1/360)th of a revolution,the angle is said to have one degree, written as 1o

.One degree is divided into 60 

minutes and one minute is divided into 60 seconds.

1

o=60’

1

’=60’’

2.Radian measure 

 

Angle subtended at the centre by an arc of length 1 

unit in a unit circle(circle of radius 1 unit) is said to 

have a measure of 1 radian( 1c ).

Relation between degree measure and radian measure

In a unit circle,one complete revolution of the initial 

side subtends an angle of 2π radians (the 

circumference) which is equal to 360o

.