Special right triangle : , which follows immediately from the Pythagorean theorem. Of all right triangles, the 45°–45°–90° degree triangle has the smallest ratio of the hypotenuse to the sum of the legs, namely . Of all right triangles, the 45°–45°–90° degree triangle has the greatest ratio of the altitude from the hypotenuse to the sum of the legs, namely . Triangles with these angles are the only possible right triangles that are also isosceles triangles in Euclidean geometry. However, in spherical geometry and hyperbolic geometry, there are infinitely many different shapes of right isosceles triangles. This is a triangle whose three angles
Priority to the right Priority to the right Priority to the right is a right-of-way system, in which the driver of a vehicle is required to give way to vehicles approaching from the right at intersections. The system is stipulated in Article 18.4.a of the Vienna Convention on Road Traffic for countries where traffic keeps to the right and applies to all intersections where it is not overridden by priority signs (uncontrolled intersections), including side roads and roundabouts (but not paths or earth-tracks). The system is widely used in countries with right-hand traffic, including most European countries. What varies, however, is the prevalence of