Find .
The function .
The point is on the circle.
.
Compare the equation with .
Radius of the circle .
Substitute and
in the above equation.
and
.
and
.
Since the angle lies on second quadrant, the value of .
The point is on a circle of radius
.
From the figure, angle lies in third quadrant.
.
Half-angle formula :
Apply the formula .
Substitute ,
and
in
.
Substitute in
.
Therefore, .
.