Length of radius of the circle:
{(-root(3))^2 + 1^2}^1/2
= {3+1}^1/2
= 2

Angle made between lines BO and the y axis:
cos x = 1/2 (adj/hyp)
x = 60 deg

Therefore angle made between y axis and AO:
90 - 60 = 30

Length of AO = 2

So x co-ordinate of A = 2 sin 30 = 1

OA?

There must be a quicker way of doing that. but this checks it.