mathscircles
posted by anoynomous .
a circle having a centre O has a triangle PQS inside it with the base QP is not on centre O. PT and QT are two tangents from an exterior point T (S, O and T are linear points  lie in one line )
it is given that angle ptq = 25 deg . find angle PSQ and OPQ

Take a look at paragraph 5 of
http://www.regentsprep.org/Regents/math/geometry/GP15/CircleAngles.htm