I'm having some trouble figuring out this apparently easy question:

Two circles touch internally at $T$. $TP$ is a chord of the smaller circle and the tangent at $P$ cuts the larger circle at $A$ and $B$ respectively. Prove that $PT$ bisects $\angle{ATB}$.
My current idea is to prove that $\triangle{APT}$ and $\triangle{BPT}$ are similar, however I cannot figure out how to do so.
