Question 15
The segment $AB$ of length $16~\mathrm{cm}$ is a diameter of a circle with centre $O$. A secant line cuts the circle at $C$ and $D$ and the line $AB$ at $P$, as shown in the figure below. If $OD = DP$ and $\angle APC = 18^\circ$, what is the measure of the angle $\angle AOC$?
