Question 28
Two circles $C_1$ and $C_2$ of radii $10$ cm and $8$ cm respectively are tangent to each other internally at a point $A$. $AD$ is the diameter of $C_1$ and $P,M$ are points on $C_1,C_2$ respectively such that $PM$ is tangent to $C_2$, as shown in the figure below. If $PM=\sqrt{20}$ cm and $\angle PAD=x^\circ$, find the value of $x$.
