The expert phase is different for different tasks. The calculator tries to calculate the sizes of three sides of the triangle from the entered data. He gradually applies the knowledge base to the entered data, which is represented in particular by the relationships between individual parameters of the triangle. These are successively applied and combined, and the parameters of the triangle calculate. Calculator iterate until the triangle has calculated all three sides. For example, the appropriate height is calculated from the given area of the triangle and the corresponding side. From the known height and angle, the adjacent side, etc., can be calculated. They use knowledge, e.g., formulas (relations) Pythagorean theorem, Sine theorem, Cosine theorem, Heron's formula, solving equations and systems of equations.The second stage is the calculation of the properties of the triangle from the known lengths of its three sides.
