Kevin C. answered 06/05/15
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Successful Math Tutor -- Recently retired high school math teacher
AB is a chord bisected by PO, the radius since OT is an angle bisector. The arcs PA and PB are also congruent since the arc AB is bisected also.
Tangent TA and chord AB intercept arc PA and is half its measure.
Chord PA and chord AB intercept arc PB and is half its measure.
Since the arcs are equal, so are the angles.
I hope this makes sense.