A rectangle is a quadrilateral whose angles are all right angles. The opposite sides of a rectangle are parallel and equal in length. Any side can be chosen as the base and the altitude is the length of a perpendicular line segment between the base and the opposite side (see Figure 1). A diagonal is either of the line segments joining opposite vertices.
The area of a rectangle with sides a and b is a×b, the perimeter is a+b, and the length of the diagonal is
A square is a special case of a rectangle where all of the sides are of equal length.