, H.2024-09-042024-09-042003-06-01Teaching Mathematics and Computer Science, Vol. 1 No. 1 (2003) , 111-1231589-7389https://hdl.handle.net/2437/379497The main topic of this paper is the investigation of 5-pentagons whose interior angles are all right angles within the hyperbolic geometry (so-called 5-rectangles). Some knowledge of elementary hyperbolic geometry is required. At first the existence of such a polygon is shown by construction within the Kleinmodel. Then two formulas due to D. M. Y. Sommerville [3] are proved. This means to juggle with trigonometric formulas of hyperbolic geometry. In the last years a big number of papers concerning hyperbolic geometry was published. This proves that the interest in this nice discipline is growing again.application/pdfhyperbolic geometryKlein-modelright-angled pentagons (Hyperbolische GeometrieKlein-Modellrechtwinklige 5-Ecke)folyóiratcikkOpen AccessH. Zeitlerhttps://doi.org/10.5485/TMCS.2003.0007Teaching Mathematics and Computer Science11Teach. Math. Comp. Sci.2676-8364