Let AB be a diameter of a circle with centre O and length 10 cm. Tangents are drawn to the circle at A and B.
a. (i) Prove that the two tangents are parallel.
b. (ii) Find the distance between these two tangents.
c. (iii) A point C is taken on the tangent at A such that AC=6 cm. Find the length of the perpendicular drawn from O to the line AC and justify your result.