The rectangle is the flat geometrical figure consisting of four points connected among themselves by pieces so that they are not crossed anywhere, except these points. It is possible to define a rectangle and other ways. This figure is basic for geometry, there are its various subspecies possessing special characteristics.
It is possible to give definition to a rectangle through a parallelogram. If all its corners are equal to 90 degrees, that is are straight lines, then it is possible to call such parallelogram a rectangle. If it is about Euclidean geometry, then a sufficient condition is existence of three right angles as the fourth in this case automatically will be equal 90th degree. The sum of corners of a quadrangle is not always equal in some types of geometry to 360 degrees therefore there can not be no rectangles at all. As it is clear from definition through a parallelogram, the rectangle is a subset of this type of geometrical figures on the plane. Therefore, all properties of a parallelogram can also precisely be applied also to rectangles. For example, all its opposite sides are parallel. All parties of a rectangle are also its heights as are located at an angle in 90 degrees to each other. If in a rectangle to construct diagonal, then it will turn out that it breaks a figure into two equal rectangular triangles therefore, according to Pythagorean theorem, the square of diagonal is equal to the sum of squares of the parties. If to enter a rectangle in a circle, then it will turn out that its diagonals coincide with diameter, and on their crossing there will be a center of a circle. There are rectangles at which all parties are equal – then such figures are called squares. Also the square can be defined how a rhombus with right angles. If the rectangle is not a square, then it has longer parties and less long. The first couple is the length of a figure, and the second – its width. The area of a rectangle is calculated so: width is multiplied by length. To find perimeter, too it is enough to know width and length, it is necessary to put them and to increase by two. If there is a figure, and it is necessary to prove that it is a rectangle, then it is the simplest to find out at first that it is a parallelogram, and then to check it for one of conditions: 1. All corners of a figure are equal to 90 degrees. 2. Diagonals of a parallelogram have equal length.3. The square of diagonal is equal to the put squares of two adjacent parties.