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The sum of the opposite angles in a rectangle is ${360}^{\circ }$.

The sum of the interior angles of a convex n-gon is $(n-2)\cdot {180}^{\circ }$.

If there is just one pair of sides parallel in a quadrilateral and the other side is perpendicular to them, then the quadrilateral is a right-angled trapezium.

At least one of the interior angles in a trapezium is obtuse.