The way of calculation of the unknown party of a triangle depends not only on task conditions, but also on for what it becomes. Not only school students at geometry lessons, but also the engineers working in the different industries of production, interior designers, cutters and representatives of many other professions face a similar task. Accuracy of calculations for the different purposes can be different, but their principle remains to the same, as in the school book of problems.

"Correct" call a triangle which all parties are equal among themselves, as well as corners in its tops. In Euclidean geometry the corners in tops of such triangle do not need calculations - they are always equal 60 °, and length of the parties can be calculated on rather simple formulas.

Geometrical problems of any level of high level of complexity assume presence at the person of ability to solve elementary problems. Otherwise the possibility of obtaining the required result considerably decreases. Besides process of almost intuitive fumbling of the correct way conducting to a result necessary to you you with need have to be able to count the areas, to know a large number of auxiliary theorems, to freely carry out calculations in the coordinate plane.

The rectangular triangle is made by two acute angles which size depends on lengths of the parties and also one corner always of invariable size 90 °. It is possible to calculate the size of an acute angle in degrees with use of trigonometrical functions or theorems of the sum of corners in triangle tops in Euclidean space.