Africa
(There are no railways in Central African Republic, Chad, Niger)
Asia
Australasia
Europe
North America
South America & Central America
See also: Transportation by country, Lists_of_companies
... square roots of both sides yields <math>x+\frac{b}{2a}=\frac{\pm\sqrt{b^2-4ac}}{2a}.</math> Subtracting b/(2a) from ...