1) Prof. DSc. Jordan Tabov, 2) Dr. Asen Velchev, Assist. Prof.
3) Dr. Stanislav Stefanov, Assist. Prof 4) Haim Haimov, MSc math.
1) Institute of Mathematics and Informatics -Bulgarian Academy of Sciences
2) Technical University – Sofia
3) University of Archtecture, Civil Engineering and Geodesy - Sofia, Bulgaria
4) 16, Bratya Shkorpil Str. - Varna, Bulgaria
Absract. Here we derive formula for the area of a quadrilateral with angle 45º between the diagonals, which is a special case of a more general formula for the area of a quadrilateral (Haimov 2022). Along the way we obtain formulas for the area of triangles with angle of 45º/135º. We also give formulas for the area of specific kinds of pentagons and hexagons, in the form of problems.
Keywords: formula for the area оf a quadrilateral; pentagon; hexagon