Rectangle - perimeter and area

A rectangle is a four-sided polygon, a special type of quadrilateral in which every interior angle measures exactly 90 degrees. Its opposite sides are equal in length and parallel to each other, while adjacent sides meet at right angles. The two diagonals of a rectangle are equal in length and bisect each other, splitting the shape into congruent triangles. Because a square is simply a rectangle whose four sides happen to be equal, the square counts as a special case of the rectangle. This regular, predictable structure makes the rectangle one of the most fundamental shapes in geometry. In everyday life it appears almost everywhere, from screens, books, and doors to windows, tables, and building plans. That is why architects, designers, engineers, and students rely on it constantly when measuring surfaces, laying out spaces, or estimating materials.