Ad contains the point o (center of the circle) and is therefore the median of the triangle abc and since it is perpendicular to bc it means that the traingle abc is an isosceles triangle...the rest is easy...
Easiest seems to be using the angles properties of a circle.
- angles on the same arc are equal,
- angle at the centre is twice the angle at the circumference,
- angle in a semi-circle is a right angle.
Call angle ABC and using the third and first of these properties you should be able to fill in all of the other angles, (in terms of