Trigonometry XI Summary

•  Trigonometry is that branch of mathematics which deals with the measurements of sides and angles of triangles.

• The figure obtained by rotating a given ray about its end point is called an angle.

• An angle is called positive if the direction of rotation of ray from initial side to terminal

             side is anti-clockwise.

• An angle is called negative if the direction of rotation of ray from initial side to terminal

             side is clockwise.

• Sexagesimal system

1 right angle = 90^o (degrees)

1 degree = 60' (minutes)

1 minute = 60'' (seconds)

• Circular system

The circular measure of an angle is the number of radians it contains where one radian

             is defined as the angle subtended at the centre of a circle by an arc whose length is

             equal to the radius.

• 180^o = p radians .

• The circular measure (q) of the angle subtended at the centre of the circle of radius r by an arc of length l is equal to l/r i.e., q = 1/r.

Each interior angle of a regular polygon of n sides is equal to

• The following rules helps in evaluating t-ratios of the angles:

• The positive and negative sign of t-ratios of

             below:

• Addition and subtraction formulae

• Transformation of product into sum or difference.

• Transformation of sum or difference into product

• T-ratios of multiple and submultiple angles