Concept:A quadrilateral with opposite sides equal and all interior angles 90∘ is a rectangle.Explanation:Let the vertices be A(9,0), B(9,6), C(−9,6), and D(−9,0).Use the distance formula: d=(x2−x1)2+(y2−y1)2.Side AB=(9−9)2+(6−0)2=0+36=6 units.Side BC=(−9−9)2+(6−6)2=(−18)2+0=18 units.Side CD=(−9−(−9))2+(0−6)2=0+36=6 units.Side DA=(9−(−9))2+(0−0)2=182+0=18 units.Thus, opposite sides are equal: AB=CD=6 and BC=DA=18.The horizontal and vertical sides are perpendicular, so each interior angle is 90∘.Since opposite sides are equal and all angles are right angles, but adjacent sides are unequal, the figure is not a square; it is a rectangle.