RECTANGLES, SQUARES, AND PARALLELOGRAMS Rectangles, squares, and parallelograms are types of quadrilaterals—four-sided geometric figures. Here are five characteristics that apply to all rectangles, squares, and parallelograms: The sum of the measures of all four interior angles is 360°. Opposite sides are parallel. Opposite sides are congruent (equal in length). Opposite angles are congruent (the same size, or equal in degree measure). Adjacent angles are supplementary (their measures total 180°). A rectangle is a special type of parallelogram in which all four angles are right angles (90°). A square is a special type of rectangle in which all four sides are.
