# Trigonometric Functions and Identities Index

## Right angled triangle and Application of right angled triangle

Right Angled Triangle:   In a right angled triangle, ABC with sides BC = a CA = b and AB = c ;     We know that: or , And or , And or ,   It is obvious that SIN A = COS B , COS A = SIN B because: A+B = 90 , So A is the complement angle of B , this may be stated as: Sine of the angle A = Sine of the complement of B So , Sine of the angle A = CoSine of angle B Or , And similarly: and     In a triangle , there are three angles and three sides. They are known as the six components or elements of a...

## Trigonometric functions of negative angles

Trigonometric functions of negative angles:   let and be any two angles equal in magnitude but opposite in sign. If we place each of them in the standard position it can be observed that the two angles are symmetrically placed on either side of x-axis. Suppose we construct a circle of radius “r” with centre “o” , it will cut the terminal arms of angles and as shown in figure below:   Let thee points “P” and “P’” respectively. Clearly , the abscissa of P is the same as that of...

## Pythagorian Identities

Let “OPQ” be a triangle where angle POQ is , and it’s base be “x” and perpendicular “y” as shown in the picture below:   Then, Appealing to the Pythagorian theorem, we have: Now let us suppose op be “r” then: And as: and   We have: Thus: This is called the fundamental Pythagorian identity of trigonometry. From this we can also develop other identities as:   Dividing both side of fundamental Pythagorian identity by   Hence ,   And now dividing both...