Rectangle

In geometry, a rectangle is defined as a four-sided figure where all four of its angles are right angles.

From this definition, it follows that a rectangle has two pairs of parallel sides; that is, a rectangle is a quadrilateral. A square is a exceptional kind of rectangle where all four sides have equal length; that is, a square is both a rectangle and a rhombus. A rectangle that is not a square is colloquially known as an four-sided figure.

Normally, of the two opposite pairs of sides in a rectangle, the duration of the longer side is called the length of the rectangle, and the duration of the shorter side is called the width. (Exception: For rectangular steel sheets, the rolling direction is called length, even if it is the shorter side.)

The area of a rectangle is the multiplication of its length and its width; in symbols, A = lw. For example, the area of a rectangle with a length of 6 and a width of 5 would be 30, because 6*5=30

In a rectangle the diagonals cross each others at their respective midpoints, under the same argument as for parallelograms. And unlike general parallelograms the two diagonals of a rectangle have the same length, the length of the diagonal can be found using the Pythagorean theorem.

In calculus, the Riemann fundamental can be thought of as a limit of sums of the areas of arbitrarily thin rectangles.