An isosceles triangle is a type of triangle which has two sides equal, the base angles of this triangle are also equal or congruent.
From the Isosceles triangle theorem, the perpendicular bisector of the base of an isosceles triangle also bisects the vertex angle. Thus, SR = RQ and ∠STR = ∠QTR .
Thus; angle QRT is right angled, as TR acts as a perpendicular bisector of the base. Also SRT =QRT