Answer:
We cannot determine whether the quadrilateral QRST is rectangle or not.
Explanation:
A quadrilateral has four vertices. It may by square, rectangle, trapezium, parallelogram, rhombus, etc.
In quadrilateral QRST, QS and RT are diagonals of QRST.
It is given that the diagonals are same.
The diagonals of square, rectangle, isosceles trapezoid are same. Therefore by given information we cannot say that the quadrilateral QRST is a rectangle.
The different quadrilaterals are shown in below figure and these quadrilaterals have congruent diagonals.
Therefore if the diagonals are same then the quadrilateral may or may not be rectangle.