total: 240,000 km mainline routes (nongovernment owned), standard gauge (1.435 m) (1989)
See also Transportation in the United States.
... square roots of both sides yields <math>x+\frac{b}{2a}=\frac{\pm\sqrt{b^2-4ac}}{2a}.</math> Subtracting b/(2a) from both sides, w ...