Define secant of a circle.

$PQ$ and $PT$ are tangents to a circle with centre $O$ and radius $5 \mathrm{cm}$. If $PQ=12 \mathrm{cm}$, then prove that the perimeter of the quadrilateral $PQOT$ is $34 \mathrm{cm}$.

In the adjoining figure, $PS$ and $PT$ are tangents to the circle drawn from an external point $P$. $CD$ is a third tangent touching the circle at $Q$. If $PT=10 \mathrm{cm}$ and $CQ=2 \mathrm{cm}$, find the perimeter of $∆PCD$.