The Chinese phrase Four Great Ancient Capitals of China (中国四大古都 pinyin zhong1 guo2 si4 da4 gu3 du1) refers to Nanjing, Beijing, Xi'an, and Luoyang.
... real. (Geometrically, this means that the parabola intersects the x-axis in two points.) If the discriminant is negative, then there are two different solutions x, both of ...