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 = √(x2 + y2)= 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.