
The diagram shows a circle of radius r with its centre at the
origin.
A rotating radius OP rotates through an angle q from the xaxis. 

The angle q is


Let (x, y) be the coordinates of the point P.� The trigonometric functions are defined as follows.












� 2 
� �2 
� 2 






� 2 
� 
� 2 






� �3 






The basic angle is the acute angle between a rotating radius and the
xaxis.
Thus 0� � basic angle � 90�. 
If a is the basic angle of q, then
If the sum of two acute angle is 90�,
they are said to be complementary angles of each other.
In general, for any angle q,

The graphs of sin x, cos x and tan x should be memorised.� Other trigonometric graphs may be generated from them by translations, scalings, reciprocal or a mixture of these transformations.