suorakaide

Suorakaide, in geometry, is the rectangle. It is a four-sided polygon with all interior angles equal to 90 degrees. A rectangle is a type of parallelogram: opposite sides are parallel and equal in length.

Key properties include that the diagonals are equal in length and bisect each other, and all four vertices lie on a circle, making a rectangle a cyclic quadrilateral. This combination of features distinguishes it from other quadrilaterals.

If the adjacent sides have lengths a and b, the area is A = a × b and the perimeter is P = 2(a + b). The diagonal length is d = sqrt(a^2 + b^2). These formulas apply regardless of the rectangle’s orientation, whether axis-aligned or rotated.

A rectangle becomes a square when a = b; in that case all sides are equal and the diagonals equal a√2. Despite the special case, every square is also a rectangle, but not every rectangle is a square.

In practical terms, rectangles model many everyday shapes and are common in design, architecture, computer graphics, and tiling. In coordinate geometry, an axis-aligned rectangle can be defined by its four corners (x1,y1), (x2,y1), (x2,y2), (x1,y2), with x1 < x2 and y1 < y2. The term suorakaide is used in Finnish to denote this shape.