Final Answer:
The value of

Step-by-step explanation
In a square, all four angles are right angles, each measuring \( 90^\circ \). This characteristic defines a square and sets it apart from other quadrilaterals. Considering the angles in cuadrilateral ABCD, all angles (\( \angle A, \angle B, \angle C, \angle D \)) are
each.
The sum of the interior angles in any quadrilateral is \( 360^\circ \). In the case of a square, with each angle being \( 90^\circ \), the total is
Therefore, \( x \) in cuadrilateral ABCD is

This property is fundamental to the geometric definition of a square and holds true in any square configuration, making \( x \) equal to
in this specific cuadrilateral.