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CHAPTER 1 : CIRCULAR FUNCTIONS AND TRIGONOMETRY

The word Trigonometry is derived from two Greek words - 'trigon' (meaning a triangle) and `metron' (meaning a measure) and hence literally Trigonometry means the measurement of a triangle. Thus it is that branch of mathematics which deals with the measurement of the sides and angles of a triangle and the investigation of various relations which exist among them.

1.1 Angles (Radians and Degrees)

Note that the definition says "an angle". This is because in the given configuration the initial side may be rotated clock-wise or counter clockwise, and it may be rotated completely around once or several times before resting at the terminal side.

 

Following figure shows a few of angles determined by same configuration.

Click here to enlarge

An angle so generated is called positive (+ve) if the direction of rotation (indicated by curved arrows) is counter clockwise and negative (-ve) if the direction of rotation is clockwise.

(2) Zero angle and straight angle : If the ray OX does not rotate at all i.e. ray OP coincides with OX without rotation then ÐXOP is a zero angle. When rotation takes place, the angle so formed can be measured in terms of the amount of rotation. One full rotation in counter clockwise sense describes an angle of 3600 of Sexagesimal system (or the English System). Hence, one half of complete rotation is the angle of 1/2 (3600 ). This angle is called straight angle since ray OX and OP are in straight line but in the opposite direction.

 

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Index

1.1 Angles (Radians & Degrees)
1.2 Arc Length & Area of the circle
Supplementary Problems

Chapter 2





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