In the co-ordinate plane, consider a point A on the positive side of x-axis. Let this point revolve about the origin in the anti-clockwise direction through an angle θ and reach the point P.

OL = x = Adjacent side

PL = y = Opposite side

OP = √(x^{2} + y^{2})= Hypotenuse (= r > 0)

The six trigonometrical ratios or circular functions are defined as:

**sin θ** = y/r

**cosec θ** = r/y

**cos θ** = x/r

**sec θ** = r/x

**tan θ** = y/x

**cot θ** = x/y

cosec θ, sec θ and cot θ are the reciprocals of sin θ, cos θ and tan θ respectively.

### Signs of T-Functions

### T-Ratios of Particular Angles