Knowledge of only one parameter (corner sizes) is not enough for finding of the area of a triangle. If there are any additional sizes, then for determination of the area it is possible to choose one of formulas in which as one of the known variables also corner size is used. Several such formulas applied are most frequent, given below.

The triangle is the simplest of polygonal flat figures which can be set by means of coordinates of points in tops of its corners. The plane land area which will be limited to the parties of this figure in the Cartesian system of coordinates can be calculated in several ways.

Triangle and rectangle - two simplest flat geometrical figures in Euclidean geometry. In the perimeters formed by the parties of these polygons some site of the plane which area can be determined in many ways is concluded. The choice of a way in each case will depend on the known parameters of figures.

Versatile triangle is called such triangle which lengths of the parties are not equal among themselves. At the same time it is meant that no two parties are equal (otherwise the triangle would turn out isosceles). For calculation of the area of a versatile triangle several different formulas are used. All main options which can meet in practice and at the solution of geometrical tasks are considered.