The quadrilateral is cyclic, because the angle that the tangent and the radius meet forms a right angle. Since the two opposite angles are 90° each, they form a 180° summation. Thus, the four points are cyclic.
Now, the smaller ∠O is 135, which means x is 180 - 135 because the four points are concyclic. Thus ∠O + x = 180°
Hence, x = 180 - 135 = 45°
∴ x = 45°
