$P$ is a point in the exterior of $\odot(O, r)$ and the tangents from $P$ to the circle touch the circle at $X$ and $Y$. Find $m \angle XPO$,if $m \angle XOY = 100^\circ$. (in $^\circ$)

$\overline{AB}$ is a chord of $\odot(O, 10)$ such that $AB = 16$. Tangents at $A$ and $B$ to the circle intersect at $P$. Find the length of $PA$.

$\overline{ PA }$ and $\overline{ PB }$ are the tangents to $\odot( O , r)$ drawn from a point $P$ outside a circle. If $m \angle APB = 65^{\circ}$,then $m \angle AOB = \ldots \ldots \ldots . .$ (in $^{\circ}$)

As shown in the figure,$AB$,$AC$ and $\overleftrightarrow{PQ}$ are tangents to the circle. If $AB = 6$,then the perimeter of $\Delta APQ = \ldots \ldots \ldots$.

If the measure of the angle between two radii of the circle is $48^{\circ}$,then the measure of the angle between the tangents drawn at the end points of the radii is $\ldots \ldots \ldots$ (in $^{\circ}$)

In the figure,common tangents $AB$ and $CD$ to two circles intersect at $E$. Prove that $AB = CD$.